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authorTim Chen <tim.c.chen@linux.intel.com>2006-07-30 03:04:02 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-07-31 13:28:42 -0700
commit3c829c367a1a52550378584a657768217971e587 (patch)
tree78dfcbe28e6a0db56992ce5ad5891398a9743bf4 /kernel/softirq.c
parent953a7f20667a8b6217ea2ac49c0877e957a0130a (diff)
[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>
Diffstat (limited to 'kernel/softirq.c')
-rw-r--r--kernel/softirq.c18
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);

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