softirq: reduce latencies

Date	Thu, 03 Jan 2013 23:49:40 -0800

In various network workloads, __do_softirq() latencies can be up
to 20 ms if HZ=1000, and 200 ms if HZ=100.

This is because we iterate 10 times in the softirq dispatcher,
and some actions can consume a lot of cycles.

This patch changes the fallback to ksoftirqd condition to :

- A time limit of 2 ms.
- need_resched() being set on current task

When one of this condition is met, we wakeup ksoftirqd for further
softirq processing if we still have pending softirqs.

Using need_resched() as the only condition can trigger RCU stalls,
as we can keep BH disabled for too long.

I ran several benchmarks and got no significant difference in
throughput, but a very significant reduction of latencies (one order
of magnitude) :

In following bench, 200 antagonist "netperf -t TCP_RR" are started in
background, using all available cpus.

Then we start one "netperf -t TCP_RR", bound to the cpu handling the NIC
IRQ (hard+soft)

Before patch :

RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=550110.424
MIN_LATENCY=146858
MAX_LATENCY=997109
P50_LATENCY=305000
P90_LATENCY=550000
P99_LATENCY=710000
MEAN_LATENCY=376989.12
STDDEV_LATENCY=184046.92
After patch :

RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=40545.492
MIN_LATENCY=9834
MAX_LATENCY=78366
P50_LATENCY=33583
P90_LATENCY=59000
P99_LATENCY=69000
MEAN_LATENCY=38364.67
STDDEV_LATENCY=12865.26

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Miller <davem@davemloft.net>
Cc: Tom Herbert <therbert@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
fs: vfat: reduce the worst case latencies

When a block partition is mounted with FAT file system
and MS_DIRSYNC option is used, some file system operations
like create, rename shall sleep in caller's context until
all the metadata have been committed to the non-volatile memory.
Since this operation is blocking call for user context,
the WRITE_SYNC option must be used instead of WRITE
(async operation) which incur inherent latencies while
flushing the meta-data corresponding to directory entries

Change-Id: I41c514889873a39d564271db0a421e6c66e5ae33
Signed-off-by: xiaogang <xiaogang@codeaurora.org>
jiffies conversions: Use compile time constants when possible

Date	Fri, 04 Jan 2013 13:15:43 -0800

Do the multiplications and divisions at compile time
instead of runtime when the converted value is a constant.

Make the calculation functions static __always_inline to jiffies.h.

Add #defines with __builtin_constant_p to test and use the
static inline or the runtime functions as appropriate.

Prefix the old exported symbols/functions with __
kernel: Prevent unnecessary rfkill event generation.

Prevent unnecessary rfkill event generation when the state has
not actually changed. These events have to be delivered to
relevant userspace processes, causing these processes to wake
up and do something while they could as well have slept. This
obviously results in more CPU usage, longer time-to-sleep-again
and therefore higher power consumption.

Change-Id: I3ac4e141fbdf1315b74d3bad6aa96f34b00c3f92
CRs-fixed: 398283
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Signed-off-by: Mykyta Iziumtsev <nikita.izyumtsev@gmail.com>
Signed-off-by: Deepthi Gowri <deepthi@codeaurora.org>
Patch-mainline: v3.7
Git-commit: eab48345c2b2d791159aaac4a77000baa8dbc1ae
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
build with ccache + fixes of some old error
Revert "Ancora: More RAM size"

This reverts commit 67bfcf2ea93586b98dcadeb8b9e1a376cc41487f.
cpufreq: Add cpu-boost driver

When certain bursty and important events take place, it might take a while
for the current cpufreq governor to notice the new load and react to it.
That would result in poor user experience. To alleviate this, the cpu-boost
driver boosts the frequency of a CPU for a short duration to maintain good
user experience while the governor catches up.

Specifically, this commit deals with ensuring that when "important" tasks
migrate from a fast CPU to a slow CPU, the frequency of the slow CPU is
boosted to be at least as high as the fast CPU for a short duration.

Since this driver enforces the boost by hooking into standard cpufreq
ADJUST notifiers, it has several advantages:
- More portable across kernel versions where the cpufreq internals might
  have been rewritten.
- Governor agnostic and hence works with multiple governors like
  conservative, ondemand, interactive, etc.
- Does not affect the sampling period/logic of existing governors.
- Can have the boost period adjusted independent of governor sampling
  period.

Change-Id: Ibd814a20043d0aba64ee7637a4a79b9ffa1b0991
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: Add a sync limit to cpu-boost

Perform frequency synchronization only when source CPU's frequency
is less than sync_threshold, else sync to the sync_threshold.

Change-Id: I544c414568d4e015b80ce5891dd215275bac95da
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Update Default Config + CPU-boost Fixes