The patch titled
timer stats: speedups
has been added to the -mm tree. Its filename is
timer-stats-speedups.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: timer stats: speedups
From: Ingo Molnar <mingo@xxxxxxx>
Make timer-stats have almost zero overhead when enabled in the config but
not used. (this way distros can enable it more easily)
Also update the documentation about overhead of timer_stats - it was
written for the first version which had a global lock and a linear list
walk based lookup ;-)
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/hrtimer/timer_stats.txt | 7 ++++---
kernel/time/timer_stats.c | 7 ++++++-
lib/Kconfig.debug | 5 ++++-
3 files changed, 14 insertions(+), 5 deletions(-)
diff -puN Documentation/hrtimer/timer_stats.txt~timer-stats-speedups Documentation/hrtimer/timer_stats.txt
--- a/Documentation/hrtimer/timer_stats.txt~timer-stats-speedups
+++ a/Documentation/hrtimer/timer_stats.txt
@@ -2,9 +2,10 @@ timer_stats - timer usage statistics
------------------------------------
timer_stats is a debugging facility to make the timer (ab)usage in a Linux
-system visible to kernel and userspace developers. It is not intended for
-production usage as it adds significant overhead to the (hr)timer code and the
-(hr)timer data structures.
+system visible to kernel and userspace developers. If enabled in the config
+but not used it has almost zero runtime overhead, and a relatively small
+data structure overhead. Even if collection is enabled runtime all the
+locking is per-CPU and lookup is hashed.
timer_stats should be used by kernel and userspace developers to verify that
their code does not make unduly use of timers. This helps to avoid unnecessary
diff -puN kernel/time/timer_stats.c~timer-stats-speedups kernel/time/timer_stats.c
--- a/kernel/time/timer_stats.c~timer-stats-speedups
+++ a/kernel/time/timer_stats.c
@@ -236,10 +236,15 @@ void timer_stats_update_stats(void *time
/*
* It doesnt matter which lock we take:
*/
- spinlock_t *lock = &per_cpu(lookup_lock, raw_smp_processor_id());
+ spinlock_t *lock;
struct entry *entry, input;
unsigned long flags;
+ if (likely(!active))
+ return;
+
+ lock = &per_cpu(lookup_lock, raw_smp_processor_id());
+
input.timer = timer;
input.start_func = startf;
input.expire_func = timerf;
diff -puN lib/Kconfig.debug~timer-stats-speedups lib/Kconfig.debug
--- a/lib/Kconfig.debug~timer-stats-speedups
+++ a/lib/Kconfig.debug
@@ -126,7 +126,10 @@ config TIMER_STATS
reprogrammed. The statistics can be read from /proc/timer_stats.
The statistics collection is started by writing 1 to /proc/timer_stats,
writing 0 stops it. This feature is useful to collect information
- about timer usage patterns in kernel and userspace.
+ about timer usage patterns in kernel and userspace. This feature
+ is lightweight if enabled in the kernel config but not activated
+ (it defaults to deactivated on bootup and will only be activated
+ if some application like powertop activates it explicitly).
config DEBUG_SLAB
bool "Debug slab memory allocations"
_
Patches currently in -mm which might be from mingo@xxxxxxx are
smpboot-cachesize-comparison-fix-in-smp_tune_scheduling.patch
git-kvm.patch
x86_64-irq-check-remote-irr-bit-before-migrating-level-triggered-irq-v3.patch
x86_64-irq-check-remote-irr-bit-before-migrating-level-triggered-irq-v3-fix.patch
x86_64-irq-check-remote-irr-bit-before-migrating-level-triggered-irq-v3-fix-fix.patch
fix-compat-futex-code-for-private-futexes.patch
something-goes-wrong-with-timer-statistics.patch
timer-stats-speedups.patch
only-allow-nonlinear-vmas-for-ram-backed-filesystems.patch
cpuset-remove-sched-domain-hooks-from-cpusets.patch
introduce-write_trylock_irqsave.patch
use-write_trylock_irqsave-in-ptrace_attach.patch
fix-stop_machine_run-problem-with-naughty-real-time-process.patch
cpu-hotplug-fix-ksoftirqd-termination-on-cpu-hotplug-with-naughty-realtime-process.patch
cpu-hotplug-fix-ksoftirqd-termination-on-cpu-hotplug-with-naughty-realtime-process-fix.patch
pie-randomization.patch
vdso-print-fatal-signals.patch
remove-clockevents_releaserequest_device.patch
add-a-flag-to-indicate-deferrable-timers-in-proc-timer_stats.patch
introduce-o_cloexec-take-2.patch
cfs-scheduler.patch
cfs-scheduler-vs-detach-schedh-from-mmh.patch
cfs-scheduler-v14-rc2-mm1.patch
cfs-scheduler-warning-fixes.patch
cfs-scheduler-v15-rc3-mm1.patch
sched-add-above-background-load-function.patch
mm-implement-swap-prefetching.patch
fix-raw_spinlock_t-vs-lockdep.patch
lockdep-sanitise-config_prove_locking.patch
lockdep-reduce-the-ifdeffery.patch
lockstat-core-infrastructure.patch
lockstat-core-infrastructure-fix.patch
lockstat-core-infrastructure-fix-fix.patch
lockstat-human-readability-tweaks.patch
lockstat-hook-into-spinlock_t-rwlock_t-rwsem-and-mutex.patch
detect-atomic-counter-underflows.patch
make-frame_pointer-default=y.patch
mutex-subsystem-synchro-test-module.patch
lockdep-show-held-locks-when-showing-a-stackdump.patch
kmap_atomic-debugging.patch
random-warning-squishes.patch
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