[PATCH] proofs: add num_to_str() to speed up /proc/stat

== stat_check.py
num = 0
with open("/proc/stat") as f:
        while num < 1000 :
                data = f.read()
                f.seek(0, 0)
                num = num + 1
==

perf shows

    20.39%  stat_check.py  [kernel.kallsyms]    [k] format_decode
    13.41%  stat_check.py  [kernel.kallsyms]    [k] number
    12.61%  stat_check.py  [kernel.kallsyms]    [k] vsnprintf
    10.85%  stat_check.py  [kernel.kallsyms]    [k] memcpy
     4.85%  stat_check.py  [kernel.kallsyms]    [k] radix_tree_lookup
     4.43%  stat_check.py  [kernel.kallsyms]    [k] seq_printf

This patch removes most of calls to vsnprintf() by adding num_to_str()
and seq_print_decimal_ull(), which prints decimal numbers without rich
functions provided by printf().

On my 8cpu box.
== Before patch ==
[root@bluextal test]# time ./stat_check.py

real    0m0.150s
user    0m0.026s
sys     0m0.121s

== After patch ==
[root@bluextal test]# time ./stat_check.py

real    0m0.055s
user    0m0.022s
sys     0m0.030s

[akpm@linux-foundation.org: remove incorrect comment, use less statck
in num_to_str(), move comment from .h to .c, simplify
seq_put_decimal_ull()]
[andrea@betterlinux.com: avoid breaking the ABI in /proc/stat]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrea Righi <andrea@betterlinux.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Turner <pjt@google.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
back ported from Linux 3.4-rc4 to Linux 3.0.x by faux123
[PATCH] sched: fix OOPS when build_sched_domains percpu allocation fails

From: "he, bo" <bo.he@intel.com>

Under extreme memory used up situation, percpu allocation
might fails. We hit it when system go to suspend-to-ram.

EIP: [<c124411a>] build_sched_domains+0x23a/0xad0
SS:ESP 0068:de725d04
CR2: 0000000034811000
---[ end trace d6086359b670b975 ]---
Kernel panic - not syncing: Fatal exception
Pid: 3026, comm: kworker/u:3 Tainted: G      D W
3.0.8-137473-gf42fbef #1
Call Trace:
 [<c18cc4f2>] panic+0x66/0x16c
 [<c12521a1>] ? oops_exit+0x61/0x90
 [<c1205f89>] oops_end+0xb9/0xd0
 [<c1227796>] no_context+0xc6/0x1f0
 [<c1227958>] __bad_area_nosemaphore+0x98/0x140
 [<c1204ebf>] ? dump_trace+0x7f/0xf0
 [<c1227d30>] ? pgtable_bad+0x130/0x130
 [<c1227a17>] bad_area_nosemaphore+0x17/0x20
 [<c1227fa0>] do_page_fault+0x270/0x3c0
 [<c1306afa>] ? pcpu_alloc+0x12ca/0x1300
 [<c1227d30>] ? pgtable_bad+0x130/0x130
 [<c1227d30>] ? pgtable_bad+0x130/0x130
 [<c18d09d3>] error_code+0x5f/0x64
 [<c13000d8>] ? shmem_setattr+0x198/0x230
 [<c1227d30>] ? pgtable_bad+0x130/0x130
 [<c124411a>] ? build_sched_domains+0x23a/0xad0
 [<c18d01a6>] ? _raw_spin_unlock_irqrestore+0x26/0x50
 [<c1244c37>] partition_sched_domains+0x287/0x4b0
 [<c12a77be>] cpuset_update_active_cpus+0x1fe/0x210
 [<c1673017>] ? __cpufreq_remove_dev+0x167/0x360
 [<c18cf03c>] ? down_write+0x1c/0x40
 [<c123712d>] cpuset_cpu_inactive+0x1d/0x30
 [<c127dff2>] notifier_call_chain+0x52/0x90
 [<c127e04e>] __raw_notifier_call_chain+0x1e/0x30
 [<c18b37c9>] _cpu_down+0x89/0x230
 [<c12547f9>] disable_nonboot_cpus+0x79/0x100
 [<c1299fb3>] suspend_devices_and_enter+0x133/0x2e0
 [<c129a27d>] enter_state+0x11d/0x180
 [<c129a307>] pm_suspend+0x27/0x70
 [<c129b8b6>] suspend+0x96/0x1d0
 [<c1271aa3>] process_one_work+0x103/0x400
 [<c129b820>] ? power_suspend_late+0x90/0x90
 [<c12728ac>] worker_thread+0x12c/0x4b0
 [<c123748d>] ? sub_preempt_count+0x3d/0x50
 [<c18d01a6>] ? _raw_spin_unlock_irqrestore+0x26/0x50
 [<c1272780>] ? manage_workers+0x520/0x520
 [<c1276f44>] kthread+0x74/0x80
 [<c1276ed0>] ? __init_kthread_worker+0x30/0x30
 [<c18d113a>] kernel_thread_helper+0x6/0x10
Signed-off-by: he, bo <bo.he@intel.com>
Reviewed-by: Zhang, Yanmin <yanmin.zhang@intel.com>
back ported for Linux 3.0 from Linux 3.4+ by faux123
[PATCH] sched/fair: Improve the ->group_imb logic

Group imbalance is meant to deal with situations where affinity masks
and sched domains don't align well, such as 3 cpus from one group and
6 from another. In this case the domain based balancer will want to
put an equal amount of tasks on each side even though they don't have
equal cpus.

Currently group_imb is set whenever two cpus of a group have a weight
difference of at least one avg task and the heaviest cpu has at least
two tasks. A group with imbalance set will always be picked as busiest
and a balance pass will be forced.
The problem is that even if there are no affinity masks this stuff can
trigger and cause weird balancing decisions, eg. the observed
behavior was that of 6 cpus, 5 had 2 and 1 had 3 tasks, due to the
difference of 1 avg load (they all had the same weight) and nr_running
being >1 the group_imbalance logic triggered and did the weird thing
of pulling more load instead of trying to move the 1 excess task to
the other domain of 6 cpus that had 5 cpu with 2 tasks and 1 cpu with
1 task.
Curb the group_imbalance stuff by making the nr_running condition
weaker by also tracking the min_nr_running and using the difference in
nr_running over the set instead of the absolute max nr_running.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link:
http://lkml.kernel.org/n/tip-9s7dedozxo8kjsb9kqlrukkf@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
modified for Linux 3.0 from Linux 3.4+ by faux123
[PATCH] timer: optimize apply_slack()

__fls(mask) is equivalent to find_last_bit(&mask, BITS_PER_LONG), but
cheaper.
find_last_bit was showing up high on the list when I was profiling for
stalls
on cache misses on a system with very small cache size (MIPS).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
[PATCH] scheduler: minor improvement to pick_next_highest_task_rt

From: Michael J Wang <mjwang@broadcom.com>

Avoid extra work by continuing on to the next rt_rq if the highest prio
task
in current rt_rq is the same priority as our candidate task.

Signed-off-by: Michael J Wang <mjwang@broadcom.com>
[PATCH] vsprintf: optimize decimal conversion (again)

    This patch is based upon an original from Michal Nazarewicz.

    Previous code was using optimizations which were developed
    to work well even on narrow-word CPUs (by today's standards).
    But Linux runs only on 32-bit and wider CPUs. We can use that.

    First: using 32x32->64 multiply and trivial 32-bit shift,
    we can correctly divide by 10 much larger numbers, and thus
    we can print groups of 9 digits instead of groups of 5 digits.

    Next: there are two algorithms to print larger numbers.
    One is generic: divide by 1000000000 and repeatedly print
    groups of (up to) 9 digits. It's conceptually simple,
    but requires an (unsigned long long) / 1000000000 division.
    Second algorithm splits 64-bit unsigned long long into 16-bit
chunks,
    manipulates them cleverly and generates groups of 4 decimal digits.
    It so happens that it does NOT require long long division.

    If long is > 32 bits, division of 64-bit values is relatively easy,
    and we will use the first algorithm.
    If long long is > 64 bits (strange architecture with VERY large
long long),
    second algorithm can't be used, and we again use the first one.
    Else (if long is 32 bits and long long is 64 bits) we use second
one.

    And third: there is a simple optimization which takes fast path
    not only for zero as was done before, but for all one-digit numbers.

    In all tested cases new code is faster than old one, in many cases
by 30%,
    in few cases by more than 50% (for example, on x86-32, conversion
of 12345678).
    Code growth is ~0 in 32-bit case and ~130 bytes in 64-bit case.

    Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
    Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
    Cc: Douglas W Jones <jones@cs.uiowa.edu>a
    back ported from Linux 3.4+ to Linux 3.0 by faux123
CONFIG: Version 5.2.3

Enabled KSM