lkml.org 
[lkml]   [2007]   [Mar]   [13]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateTue, 13 Mar 2007 21:06:14 +1100
FromNick Piggin <>
SubjectRe: SMP performance degradation with sysbench
Andrea Arcangeli wrote:
> On Tue, Mar 13, 2007 at 04:11:02PM +1100, Nick Piggin wrote:
> 
>>Hi Anton,
>>
>>Very cool. Yeah I had come to the conclusion that it wasn't a kernel
>>issue, and basically was afraid to look into userspace ;)
> 
> 
> btw, regardless of what glibc is doing, still the cpu shouldn't go
> idle IMHO. Even if we're overscheduling and trashing over the mmap_sem
> with threads (no idea if other OS schedules the task away when they
> find the other cpu in the mmap critical section), or if we've
> overscheduling with futex locking, the cpu usage should remain 100%
> system time in the worst case. The only explanation for going idle
> legitimately could be on HT cpus where HT may hurt more than help but
> on real multicore it shouldn't happen.
> 

Well ignoring the HT issue, I was seeing lots of idle time simply
because userspace could not keep up enough load to the scheduler.
There simply were fewer runnable tasks than CPU cores.

But it wasn't a case of all CPUs going idle, just most of them ;)

-- 
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com 

-
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: 2007-03-13 11:09    [from the cache]
©2003-2008