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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/rtmutex.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/rtmutex.c')
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