diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2013-11-19 16:13:38 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2014-01-13 13:47:36 +0100 |
| commit | 9ea4c380066fbe23fe0da7f4abfabc444f2467f4 (patch) | |
| tree | a6f3e8def29275f04b33cfb0defcefc9e0adaaf0 /kernel | |
| parent | c726099ec224be8078d91072207053ff9a1ad6fc (diff) | |
| download | linux-9ea4c380066fbe23fe0da7f4abfabc444f2467f4.tar.bz2 | |
locking: Optimize lock_bh functions
Currently all _bh_ lock functions do two preempt_count operations:
local_bh_disable();
preempt_disable();
and for the unlock:
preempt_enable_no_resched();
local_bh_enable();
Since its a waste of perfectly good cycles to modify the same variable
twice when you can do it in one go; use the new
__local_bh_{dis,en}able_ip() functions that allow us to provide a
preempt_count value to add/sub.
So define SOFTIRQ_LOCK_OFFSET as the offset a _bh_ lock needs to
add/sub to be done in one go.
As a bonus it gets rid of the preempt_enable_no_resched() usage.
This reduces a 1000 loops of:
spin_lock_bh(&bh_lock);
spin_unlock_bh(&bh_lock);
from 53596 cycles to 51995 cycles. I didn't do enough measurements to
say for absolute sure that the result is significant but the the few
runs I did for each suggest it is so.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: rui.zhang@intel.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/softirq.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index 11025ccc06dd..7500cce1ebfd 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -107,7 +107,7 @@ static void __local_bh_disable(unsigned long ip, unsigned int cnt) /* * Were softirqs turned off above: */ - if (softirq_count() == cnt) + if (softirq_count() == (cnt & SOFTIRQ_MASK)) trace_softirqs_off(ip); raw_local_irq_restore(flags); @@ -133,7 +133,7 @@ static void __local_bh_enable(unsigned int cnt) { WARN_ON_ONCE(!irqs_disabled()); - if (softirq_count() == cnt) + if (softirq_count() == (cnt & SOFTIRQ_MASK)) trace_softirqs_on(_RET_IP_); preempt_count_sub(cnt); } |