Abstract:
A thermal state within an information handling system enclosure is managed within predetermined constraints by estimating thermal energy introduced to the enclosure by power dissipation to electronic components and thermal energy removed from the enclosure by a cooling airflow generated by a fan. A desired bulk temperature of a cooling airflow is attained at a predetermined position in an enclosure by selecting a fan speed and power allocation to the components that conserves energy within the enclosure at a predetermined thermal state.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates in general to the field of information handling system thermal control, and more particularly to information handling system thermal control by energy conservation. 
         [0003]    2. Description of the Related Art 
         [0004]    As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
         [0005]    Information handling systems are typically built by assembling a variety of components into a chassis so that the components cooperate to process information. For example, a blade server information handling system has a chassis that accepts plural blade server modules by sharing power and networking resources of the chassis with the blade servers under the control of a chassis management controller (CMC). Each blade server module typically has a motherboard with one or more central processing units (CPUs), power distribution circuits, persistent storage devices like hard disk drives or solid state drives, memory like DRAM, networking components, mezzanine cards and a baseboard management controller (BMC) that provides management functions like remote power-up and power-down. The chassis management controller manages power resources by distributing power allocations to the blade modules. A baseboard management controller on each blade module powers components within the blade module to operate within the power allocation budget provided by the chassis management controller. The chassis management controller also typically manages cooling resources provided by a fan controller and one or more cooling fans based upon thermal information provided from the baseboard management controllers, such as thermal measurements at components within each blade module. In server information handling systems, a bulk air temperature represented by the temperature of a cooling airflow exhaust is sometimes managed by adjusting fan speed to maintain less than a maximum exhaust temperature. 
         [0006]    One difficulty with management of thermal conditions in an information handling system chassis is that thermal conditions tend to vary throughout a chassis enclosure. Variance in thermal conditions can be significant in a modular information handling system, such as a blade information handling system, where a particular module has a higher workload than other modules in the same chassis. Variance in thermal conditions can also be significant across an information handling system module where different components of the module operate at varying workloads. For example, thermal conditions near a central processing unit typically increase during the performance of processing-intensive operations. In order to monitor thermal conditions at processors, processors typically incorporate a thermal sensor, such as a thermistor, and logic to report thermal conditions measured by the thermal sensor to a system thermal manager, such as firmware instructions running on a BIOS, BMC, CMC, and/or fan controller that manages cooling fan operating speeds. Processors are typically physically located “upstream” of a cooling airflow provided by a cooling fan to provide efficient cooling since processors generally are one of the greatest sources of thermal energy in a chassis and also usually among the most heat sensitive of components. Other components are typically disposed in the chassis “downstream” of the processor so that cooling airflow passes by the processor first and then passes by less-heat sensitive components. 
         [0007]    One difficulty with managing thermal conditions in an information handling system chassis enclosure is that not all components integrate thermal self-protection capabilities in order to maintain reliability conformance during thermal excursions, such as when a cooling system fails, extreme ambient environmental temperatures exist or ultra-high stress operating conditions exist that exceed the capabilities of a chassis&#39; cooling system. For example, a processor operating in extreme thermal conditions will throttle its power consumption to reduce heat generation and maintain its internal temperature within a desired constraint; however, mezzanine cards, some hard disk drives and many on board devices like networking, chipset, power distribution and BMC devices, do not include thermal sensors or thermal self-protection capabilities. Since these thermally “helpless” components are often downstream of a cooling airflow, the three primary ways of ensuring adequate cooling of “helpless” components are to throttle the helpless components, to increase fan speeds so that a greater cooling airflow exists to remove excess thermal energy or to throttle upstream components so that less thermal energy is generated to reduce the downstream cooling airflow temperature. Unfortunately, if components do not have thermal sensors then no direct measurement of thermal conditions at the components exists to provide direct control over thermal conditions at the component. 
         [0008]    In order to manage thermal conditions within an information handling system chassis for components that do not include thermal sensors, some information handling systems dispose thermal sensors near components that monitor localized air temperatures. Unfortunately, as air flows through an information handling system enclosure, air streamlines across the enclosure can have significant variation in temperature even across small linear separations. In chassis enclosures that include plural modules, such as a blade chassis, an exhaust temperature of a cooling subsystem that cools plural modules does not necessarily indicate thermal conditions at any one module because different modules often run different loads. For example, a module running at a high load can have extreme thermal conditions even though the bulk temperature of a cooling subsystem exhaust is in a normal range. One solution for thermal management of components that lack thermal sensors is to nest a large array of onboard thermistors to average thermal readings for a more accurate “bulk” air temperature. This solution tends to increase system cost by the addition of plural interfaced sensors and system complexity by having multiple thermal measurements and multiple failure points. 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore a need has arisen for a system and method which measures information handling system thermal conditions to manage cooling system operation and component throttling for managing thermal conditions of components that lack thermal monitoring. 
         [0010]    In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for managing cooling system operation and component throttling to manage thermal conditions of components that lack thermal monitoring. A thermal state at a predetermined location within a chassis enclosure is managed by applying power dissipation of electronic components and inlet temperature of a cooling airflow to set a fan speed that establishes a desired cooling airflow rate. 
         [0011]    More specifically, an information handling system has plural components disposed in an enclosure that cooperate to process information. A cooling fan provides a cooling airflow from an inlet, past the components and out an outlet. The components are powered by a power supply under the direction of a power manager, which monitors power dissipated by the components. A thermal manager interfaced with the power manager and the cooling fan establishes a cooling fan speed to maintain a predetermined thermal state within the enclosure by applying power dissipation of a set of components and a temperature sensed at the cooling fan inlet. For example, in a modular information handling system having plural processing modules, such as a blade server having plural blades, the thermal manager manages the thermal state associated with a processing module by applying the power dissipated by the components of the processing module and the inlet temperature for cooling airflow to determine a cooling fan speed that will provide a sufficient cooling airflow to maintain less than a predetermined bulk temperature with the processing module. If the cooling fan cannot provide an adequate cooling airflow, then the thermal manager reduces power consumption of one or more components to maintain the desired thermal state in the processing module. For instance, the thermal module throttles a processor even though the temperature sensed at the processor is in a normal operating range so that downstream components will have adequate cooling, even though the downstream components do not have direct temperature sensing. The adequate cooling of the downstream components is ensured by 
         [0012]    The present invention provides a number of important technical advantages. One example of an important technical advantage is that thermal conditions within an information handling system enclosure are accurately measured without having to dispose an array of sensors throughout the enclosure. Measurements of enclosure thermal conditions estimated by the Law of Conservation of Energy are applied to provide thermal control for downstream components that lack thermal sensors. If thermal conditions within the enclosure exceed a threshold associated with operation of unmonitored components, the thermal conditions are managed to maintain an operating environment acceptable to the unmonitored components. For example, upstream components are throttled to reduce thermal energy released to a cooling airflow, fan speed is increased to reduce cooling airflow temperature or unmonitored components are throttled or powered down to reduce downstream thermal energy release or prevent damage to the unmonitored components. Bulk enclosure thermal energy estimates derived from the Law of Conservation of Energy combined with thermal measurements from monitored components offers a more precise overall picture of thermal operating conditions at an information handling system without unnecessary thermal sensors and system complexity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element. 
           [0014]      FIG. 1  depicts a side view of an example of an information handling system that manages a thermal state in an enclosure by adjusting fan speed based on power dissipation and cooling airflow inlet temperature; 
           [0015]      FIG. 2  depicts a functional block diagram of a process for managing an information handling system enclosure thermal state by adjusting fan speed based on power; and 
           [0016]      FIG. 3  depicts a flow diagram of a process for managing an information handling system enclosure thermal state by adjusting fan speed and power dissipation. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A thermal state within an information handling system enclosure is managed by adjusting fan speed for a cooling airflow in the enclosure based upon an inlet temperature of the cooling airflow and power dissipated to components running within the enclosure. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components. 
         [0018]    Referring now to  FIG. 1 , a side view depicts an example embodiment of an information handling system  10  that manages a thermal state in an enclosure  12  by adjusting fan speed based on power dissipation and cooling airflow inlet temperature. In the example embodiment, information handling system  10  is a blade server having plural slots  14 , each slot  14  accepting a blade information handling system module  16  that processes information. For example, each blade information handling system module  16  includes components that cooperate to process information, such as a CPU  18 , RAM  20 , a mezzanine card  22 , a hard disk drive  24 , and a chipset  26  that communicate through a motherboard  28 . The components are managed by a baseboard management controller (BMC)  30 , which selectively provides power to the components from a power supply  32  by communicating with a power manager  34 . 
         [0019]    During operation of components disposed in enclosure  12 , thermal energy is generated in varying amounts based upon the power consumption of the components. For example, under a heavy processing load, CPU  18  uses increased power and produces increased thermal energy as a byproduct of processing information. Some components, such as CPU  18 , include a temperature sensor that senses the temperature of the components during operations. Other components do not include a sensor that allows a direct indication of the component&#39;s temperature, such as some hard disk drives and mezzanine cards as well as basic electronic components disposed in motherboard  28 , like resistors and capacitors. In varying degrees, the components have power consumption managed by logic running in chipset  26  and/or on BMC  30 . For example, BMC  30  manages power consumption of CPU  18  by selectively throttling the speed at which CPU  18  executes instructions to reduce power consumption. As another example, firmware in chipset  26  under the direction of BMC  30  removes power from mezzanine card  22  and hard disk drive  24  to reduce power consumption and the associated generation of thermal energy. 
         [0020]    One or more cooling fans  36  disposed in enclosure  12  draws a cooling airflow through an inlet  38  and passes the cooling airflow over the components and out an outlet  40  to remove excess thermal energy from the components. In order to ensure proper operation of components within enclosure  12 , the thermal state within enclosure  12  is managed to stay within defined constraints, such as a maximum bulk air temperature. In the example depicted by  FIG. 1 , CPU  18  is located upstream in the cooling airflow, meaning closer to inlet  38 , since CPU  18  tends to create more excess thermal energy than other components and typically needs a cooler temperature of the cooling airflow to obtain adequate cooling. Other components are located downstream of CPU  18 , meaning closer to outlet  40 , since these components tend to produce less excess thermal energy. Downstream components obtain adequate cooling as long as the increase in cooling airflow temperatures from upstream components is not excessive; however, since some downstream components often do not have direct temperature monitoring, such as by a temperature sensor disposed in the component, inadequate cooling airflow and/or excessive thermal energy production by upstream components can result in an overtemperature at downstream components. 
         [0021]    In order to prevent an overtemperature of downstream components, a thermal manager  42  manages the speed selected for cooling fan  36  by communicating a cooling fan speed to fan controller  44 , which sets the speed at which cooling fan  36  runs. Selection of an increased cooling fan speed results in a greater airflow, typically measured in cubic feet per minute (CFM), to provide increased thermal transfer of thermal energy from components to the airflow and out outlet  40 . Thermal manager  42  selects a cooling fan speed that will maintain a predetermined thermal state within enclosure  12 , such as a bulk air temperature in the proximity of a selected set of components. The predetermined thermal state is defined to provide operating conditions within the thermal constraints of the components disposed within enclosure  12 . For example, the predetermined thermal state is associated with a bulk airflow temperature that is quantifiable by the temperature at outlet  40  or a temperature measured at various physical locations within enclosure  12 , such as in a slot  14  or the space over a blade module. 
         [0022]    Thermal manager  42  sets fan  36  speed to maintain a predetermined thermal state within enclosure  12  by applying the Law of Conservation of Energy to enclosure  12 . In summary, at a predetermined energy state, energy entered into the enclosure by dissipation of power at the components equals energy removed from the enclosure by absorption to the cooling airflow provided by fan  36 . Heating of a fluid in motion is defined as: 
         [0000]        q =( m dot)( Cp )( dT ) 
         [0000]    where q is the total energy dissipation, mdot is the mass flow rate of the energy absorbing fluid, Cp is the specific heat of the fluid, and dT represents the temperature rise of the fluid as a consequence of thermal energy input. In a typical information handling system operating condition, the density and specific heat of the cooling fluid, typically air but sometimes liquid, are constant. Assuming constant density and specific heat of air as a cooling fluid reduces the equation for conservation of energy in enclosure  12  to 
         [0000]    
       
      
       q=Q*K*dT  
      
     
         [0000]    where Q is the volumetric flow rate of the cooling fluid, such as air stated in cubic feet per minute (CFM), and K is a constant that combines specific heat and density of fluid for the units chosen for the surrounding variables. 
         [0023]    Thermal manager  42  maintains a predetermined thermal state in enclosure  12  by apply an inlet temperature measured by an inlet temperature sensor  46  and instantaneous power dissipation provided by power manager  44  to a characteristic airflow equation defined for enclosure  12  to determine a fan speed setting for fan  36 . For example, a characteristic airflow equation soft or hard coded into thermal manager  42  yields a duty cycle for fan  36 : 
         [0000]      % Duty Cycle= A 1(CFM Request)+ B 1 
         [0000]    where A1 and B1 are configuration constants describing the relationship of a given chassis between airflow in CFM and fan duty cycle speed settings. A characteristic airflow equation may be defined for any particular portion of an enclosure where a thermal state may be of interest, such as within a blade module or over a downstream portion of a processing module that lacks direct monitoring of component temperatures. 
         [0024]    If the cooling fan speed setting for a given CFM request is greater than 100%, then the cooling fan cannot provide the necessary cooling airflow to maintain a predetermined thermal state in enclosure  12  for the current power dissipation. If available cooling fan speed settings are not sufficient to maintain the predetermined thermal state, then thermal manager  42  commands a reduction in power consumption by one or more of the components disposed in enclosure  12 . Thus, even though temperatures measured at monitored components are within limits, such as a temperature measured at a CPU  18 , thermal manager  42  can throttle CPU  18  to reduce the thermal state within enclosure  12  and prevent overheating of components downstream of CPU  18 . Alternatively, thermal manger  42  can power down downstream components that lack direct monitoring of their thermal state to reduce power dissipation and thereby reduce the thermal state within enclosure  12 . In one embodiment, thermal manager  42  selects components to have a reduced power consumption based upon an amount of power dissipation reduction that will provide a thermal state within constraints given available cooling fan speed settings. For example, if a reduction of power dissipation by 10 Watts will provide the predetermined thermal state with a fan duty cycle of 100%, then thermal manager can select throttling of CPU  18  or power down of mezzanine card  22  so that power dissipation is reduced by 10 Watts. In one embodiment, thermal manager  42  selects components to have a reduced power dissipation based upon functions being performed by information handling system  10 . As an example, if current operations do not require a video card disposed on a mezzanine card  22 , then thermal manager  42  directs BMC  30  and/or chipset  26  to power down mezzanine card  22  so that throttling of CPU  18  is avoided. 
         [0025]    In one embodiment, thermal manager  42  manages the thermal state at plural points in enclosure  12 . For example, each of plural blade modules  16  is allocated power by power manager  34  to ensure that the limits of power supply  32  are not exceeded. Power manager  34  monitors power dissipation at each blade module  16  and reports the power dissipation for each blade module  16  to thermal manager  42 . Thermal manager  42  applies the power dissipation at a blade module  16  to determine the thermal state of the blade module  16  so that each blade module  16  has its thermal state individually monitored. Thermal manager  42  manages the thermal state within each blade module  16  by managing power dissipation of components of the blade module  16  based upon a characteristic airflow equation for the blade module. Thus, for example, even though enclosure  12  overall has a thermal state within predetermined constraints, an individual blade module  16  within enclosure  12  having a high workload may experience an overtemperature due to power dissipation of components at the blade module  16 . Thermal manager  42  addresses local thermal states within enclosure  12  based upon local power dissipation and local airflow characteristics to prevent local overtemperatures by throttling or powering down selected components within the local thermal state or upstream of the local thermal state. In one alternative embodiment, thermal sensors may be disposed at various locations in enclosure  12 , such as an exhaust sensor  48  or sensors within a blade module  16 , for a comparison of measured bulk temperatures with expected bulk temperatures; however, an advantage of the present disclosure is that management of a thermal state within enclosure  12  is performed without requiring temperature sensors that attempt to measure bulk air temperature after heating by components. 
         [0026]    Referring now to  FIG. 2 , a functional block diagram of a process for managing an information handling system enclosure thermal state by adjusting fan speed based on power. At step  50 , ambient air temperature is sensed at the inlet for a cooling airflow. At step  52 , power dissipation by components of an information handling system is sensed. At step  54 , ambient temperature and power dissipation are applied to a model of the information handling system to determine a thermal state. The model can apply to a complete enclosure such as to estimate bulk air temperature at an exhaust of the enclosure or to a portion of an enclosure, such as to estimate the bulk air temperature proximate a processing module, such as a server sled or blade. The thermal state that results from step  54  is applied to a cooling fan state at step  56  to determine a fan speed that will provide a cooling airflow for a desired thermal state of the bulk temperature modeled at step  54 . For example, if all cooling fans are operational, values presented in table  60  are applied for determining air flow from a fan duty cycle. If one or more of plural fans have failed, values presented in table  62  are applied for determining air flow from a fan duty cycle. In an alternative embodiment, air flow rates are determined as part of a characteristic airflow equation as described above. At step  66 , the fan duty cycle is provided that will maintain a desired thermal state for the enclosure or portion of the enclosure modeled at step  54 . At step  68 , the fan controller sets the fan speed at the determined duty cycle to control the air flow so that a desired thermal state results. 
         [0027]    Referring now to  FIG. 3 , a flow diagram depicts a process for managing an information handling system enclosure thermal state by adjusting fan speed and power dissipation. The process begins at step  70  with a fan speed setting output for maintaining a desired thermal state. At step  72 , a determination is made of whether the cooling fan can operate at the fan speed needed to maintain the desired thermal state. If the requested fan speed is available, the process continues to step  74  to set the fan speed. If at step  72  the requested fan speed exceeds an available fan speed, the process continues to step  76  to reduce power consumption at one or more components so that the fan speeded needed to maintain the desired thermal state does not exceed the available fan speed. 
         [0028]    Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.