Re: [PATCH RT 00/02] SLOB optimizations

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Ingo Molnar a écrit :
* Eric Dumazet <[email protected]> wrote:

in any case, on sane platforms (i386, x86_64) an irq-disable is well-optimized in hardware, and is just as fast as a preempt_disable().
I'm afraid its not the case on current hardware.

The irq enable/disable pair count for more than 50% the cpu time spent in kmem_cache_alloc()/kmem_cache_free()/kfree()

because you are not using NMI based profiling?

oprofile results on a dual Opteron 246 :

You can see the high profile numbers right after cli and popf(sti) instructions, popf being VERY expensive.

that's just the profiling interrupt hitting them. You should not analyze irq-safe code with a non-NMI profiling interrupt.


I'm using oprofile on Opteron, and AFAIK it's NMI based.

# grep NMI /proc/interrupts ; sleep 1 ; grep NMI /proc/interrupts
NMI:  391352095 2867983903
NMI:  391359678 2867998498

thats 7583 and 14595 NMI / second on cpu0 and cpu1 respectivly in this sample.

CLI/STI is extremely fast. (In fact in the -rt tree i'm using them within mutexes instead of preempt_enable()/preempt_disable(), because they are faster and generate less register side-effect.)

	Ingo



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