* Eric Dumazet <dada1@xxxxxxxxxxxxx> 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.)
Ingo