Re: SMP performance degradation with sysbench

Andrea Arcangeli
2007-03-13T10:31:38Z

On Tue, Mar 13, 2007 at 09:06:14PM +1100, Nick Piggin wrote:
> 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.

When you said idle I thought idle and not waiting for I/O. Waiting for
I/O would be hardly a kernel issue ;). If they're not waiting for I/O
and they're not scheduling in userland with nanosleep/pause, the cpu
shouldn't go idle. Even if they're calling sched_yield in a loop the
cpu should account for zero idle time as far as I can tell.