Messages in this thread | | | Date | Thu, 29 Jul 2010 21:57:43 +0200 | Subject | Re: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3 | From | Corrado Zoccolo <> |
| |
On Mon, Jul 26, 2010 at 4:33 PM, Vivek Goyal <vgoyal@redhat.com> wrote: > On Sat, Jul 24, 2010 at 11:07:07AM +0200, Corrado Zoccolo wrote: >> On Sat, Jul 24, 2010 at 10:51 AM, Christoph Hellwig <hch@infradead.org> wrote: >> > To me this sounds like slice_idle=0 is the right default then, as it >> > gives useful behaviour for all systems linux runs on. >> No, it will give bad performance on single disks, possibly worse than >> deadline (deadline at least sorts the requests between different >> queues, while CFQ with slice_idle=0 doesn't even do this for readers). > > Not sure if CFQ will be worse than deadline with slice_idle=0. CFQ has > some inbuilt things which should help. > > - Readers preempt Writers > - All writers go in one single queue (at one prio level), readers get > their individual queues and can outnumber writers. > > So I guess CFQ with slice_idle=0 should not be worse than deadline in terms > of read latencies.
I was thinking more to the fact that read requests are not sorted: they will basically be serviced in FIFO order, while deadline will sort them and possibly increase locality. In the reader vs writer case, cfq may have a small edge. Basically, they will severely underperform vs. cfq with slice != 0, though.
> > Vivek >
-- __________________________________________________________________________
dott. Corrado Zoccolo mailto:czoccolo@gmail.com PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- The self-confidence of a warrior is not the self-confidence of the average man. The average man seeks certainty in the eyes of the onlooker and calls that self-confidence. The warrior seeks impeccability in his own eyes and calls that humbleness. Tales of Power - C. Castaneda -- 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/
| |