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Date: Sat, 28 Jul 2007 14:36:54 +0200 From: "Dmitry Adamushko" <dmitry.adamushko@...il.com> To: tim.c.chen@...ux.intel.com Cc: "Ingo Molnar" <mingo@...e.hu>, "Linux Kernel" <linux-kernel@...r.kernel.org> Subject: Re: Volanomark slows by 80% under CFS On 28/07/07, Tim Chen <tim.c.chen@...ux.intel.com> wrote: > [ ... ] > It may make sense to queue the > yielding process a bit further behind in the queue. > I made a slight change by zeroing out wait_runtime > (i.e. have the process gives > up cpu time due for it to run) for experimentation. But that's wrong. The 'wait_runtime' might have been negative at this point (i.e. a task is in the negative 'run-time' balance wrt the 'etalon' nice-0 task). Your change ends up helping such a task to actually stay closer to the 'left most' element of the tree (or to be it) and not "further behind in the queue" as your intention is. I don't know Volanomark's details so refrain from speculating on why this change "improves" benchmark results indeed (maybe some afected tasks have positive 'wait_runtime's on average for this setup). If you want to make sure (just for a test) a yeilding task is not the left-most (at least) for some short interval of time (likely to be <= 1 tick), take a look at yield_task_fair() in e.g. cfs-v15. > Volanomark runs better > and is only 40% (instead of 80%) down from old scheduler > without CFS. 40 or 80 % is still a huge regression. > > Regards, > Tim > -- Best regards, Dmitry Adamushko - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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