Messages in this thread | | | Date | Thu, 22 Dec 2005 22:11:32 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH RT 00/02] SLOB optimizations |
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* Eric Dumazet <dada1@cosmosbay.com> 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.
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.)
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