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Date: Mon, 27 Oct 2008 11:33:06 +0000 From: Alan Cox <alan@...rguk.ukuu.org.uk> To: Ingo Molnar <mingo@...e.hu> Cc: Jiri Kosina <jkosina@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Mike Galbraith <efault@....de>, David Miller <davem@...emloft.net>, rjw@...k.pl, s0mbre@...rvice.net.ru, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [tbench regression fixes]: digging out smelly deadmen. > The way to get the best possible dbench numbers in CPU-bound dbench > runs, you have to throw away the scheduler completely, and do this > instead: > > - first execute all requests of client 1 > - then execute all requests of client 2 > .... > - execute all requests of client N Rubbish. If you do that you'll not get enough I/O in parallel to schedule the disk well (not that most of our I/O schedulers are doing the job well, and the vm writeback threads then mess it up and the lack of Arjans ioprio fixes then totally screw you) </rant> > the moment the clients are allowed to overlap, the moment their requests > are executed more fairly, the dbench numbers drop. Fairness isn't everything. Dbench is a fairly good tool for studying some real world workloads. If your fairness hurts throughput that much maybe your scheduler algorithm is just plain *wrong* as it isn't adapting to workload at all well. Alan -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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