![]() | |||||||||||||
Messages in this thread |
> Good question. Btw. - faster by what order of magnitude? pushf + popf is on K8 at least ~18 cycles, on P4 it is much more because they synchronize the pipeline there (hundreds of cycles) cpu local add would be a few cycles at best and doesn't have any impact on the pipeline > local_irq_save/restore seems to be fine for kernel/profile.c > > > Reason 1: > cpu_local_* uses __get_cpu_var, which conflicts with struct statistic > being embedded into struct xyz that is allocated whenever the client > needs it. > > I could try to use local_t in conjunction with local_add etc. > (as seen in include/linux/dmaengine.h in 2.6.17-mm6). > Does this also yield a performance gain worth consideration? Yes, but you would need preempt_disable() then. For non preemptible kernels (far majority) that would be already a big win. > So, removing local_irq_save/restore would require statistics to be > switched on and their buffers being available all the time. That is, > buffers holding counters etc. can't be allocated at run time - what > if allocation fails? (Should I leave this issue to clients?). Can't you use RCU for this? > Reason 4: > The alleged overhead of local_irq_save/restore (as compared > to atomic operations) local_* doesn't need to be atomic. IT isn't on x86 at least. On some other architectures it can be, but i think it's just a SMOP of fixing them. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
| Last update: 2006-07-06 17:05 [from the cache] ©2003-2008 | |||||||||||||