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| author | Tim Chen <tim.c.chen@linux.intel.com> | 2006-07-30 12:04:02 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-07-31 22:28:42 +0200 |
| commit | 3c829c367a1a52550378584a657768217971e587 (patch) | |
| tree | 78dfcbe28e6a0db56992ce5ad5891398a9743bf4 | |
| parent | [PATCH] Typo in ub clause of devices.txt (diff) | |
| download | linux-3c829c367a1a52550378584a657768217971e587.tar.xz linux-3c829c367a1a52550378584a657768217971e587.zip | |
[PATCH] Reducing local_bh_enable/disable overhead in irqtrace
The recent changes from irqtrace feature has added overheads to
local_bh_disable and local_bh_enable that reduces UDP performance across
x86_64 and IA64, even though IA64 does not support the irqtrace feature.
Patch in question is
[PATCH]lockdep: irqtrace subsystem, core
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=c
ommit;h=de30a2b355ea85350ca2f58f3b9bf4e5bc007986
Prior to this patch, local_bh_disable was a short macro. Now it is a
function which calls __local_bh_disable with added irq flags save and
restore. The irq flags save and restore were also added to
local_bh_enable, probably for injecting the trace irqs code.
This overhead is on the generic code path across all architectures. On a
IA_64 test machine (Itanium-2 1.6 GHz) running a benchmark like netperf's
UDP streaming test, the added overhead results in a drop of 3% in
throughput, as udp_sendmsg calls the local_bh_enable/disable several times.
Other workloads that have heavy usages of local_bh_enable/disable could
also be affected. The patch ideally should not have affected IA-64
performance as it does not have IRQ tracing support. A significant portion
of the overhead is in the added irq flags save and restore, which I think
is not needed if IRQ tracing is unused. A suggested patch is attached
below that recovers the lost performance. However, the "ifdef"s in the
patch are a bit ugly.
Signed-off-by: Tim Chen <tim.c.chen@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
| -rw-r--r-- | kernel/softirq.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index aab880677ce0..3789ca98197c 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -65,6 +65,7 @@ static inline void wakeup_softirqd(void) * This one is for softirq.c-internal use, * where hardirqs are disabled legitimately: */ +#ifdef CONFIG_TRACE_IRQFLAGS static void __local_bh_disable(unsigned long ip) { unsigned long flags; @@ -80,6 +81,13 @@ static void __local_bh_disable(unsigned long ip) trace_softirqs_off(ip); raw_local_irq_restore(flags); } +#else /* !CONFIG_TRACE_IRQFLAGS */ +static inline void __local_bh_disable(unsigned long ip) +{ + add_preempt_count(SOFTIRQ_OFFSET); + barrier(); +} +#endif /* CONFIG_TRACE_IRQFLAGS */ void local_bh_disable(void) { @@ -121,12 +129,16 @@ EXPORT_SYMBOL(_local_bh_enable); void local_bh_enable(void) { +#ifdef CONFIG_TRACE_IRQFLAGS unsigned long flags; WARN_ON_ONCE(in_irq()); +#endif WARN_ON_ONCE(irqs_disabled()); +#ifdef CONFIG_TRACE_IRQFLAGS local_irq_save(flags); +#endif /* * Are softirqs going to be turned on now: */ @@ -142,18 +154,22 @@ void local_bh_enable(void) do_softirq(); dec_preempt_count(); +#ifdef CONFIG_TRACE_IRQFLAGS local_irq_restore(flags); +#endif preempt_check_resched(); } EXPORT_SYMBOL(local_bh_enable); void local_bh_enable_ip(unsigned long ip) { +#ifdef CONFIG_TRACE_IRQFLAGS unsigned long flags; WARN_ON_ONCE(in_irq()); local_irq_save(flags); +#endif /* * Are softirqs going to be turned on now: */ @@ -169,7 +185,9 @@ void local_bh_enable_ip(unsigned long ip) do_softirq(); dec_preempt_count(); +#ifdef CONFIG_TRACE_IRQFLAGS local_irq_restore(flags); +#endif preempt_check_resched(); } EXPORT_SYMBOL(local_bh_enable_ip); |