From 9ea4c380066fbe23fe0da7f4abfabc444f2467f4 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 19 Nov 2013 16:13:38 +0100 Subject: 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 Signed-off-by: Peter Zijlstra Cc: jacob.jun.pan@linux.intel.com Cc: Mike Galbraith Cc: hpa@zytor.com Cc: Arjan van de Ven Cc: lenb@kernel.org Cc: rjw@rjwysocki.net Cc: rui.zhang@intel.com Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/softirq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/softirq.c') 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); } -- cgit v1.2.3-55-g7522