Messages in this thread | | | Date | Tue, 13 May 2008 15:05:09 +0200 | From | Jens Axboe <> | Subject | Re: performance "regression" in cfq compared to anticipatory, deadline and noop |
| |
On Tue, May 13 2008, Matthew wrote: > On Tue, May 13, 2008 at 2:20 PM, Jens Axboe <jens.axboe@oracle.com> wrote: > > > > On Sun, May 11 2008, Kasper Sandberg wrote: > > > On Sun, 2008-05-11 at 14:14 +0100, Daniel J Blueman wrote: > > > > I've been experiencing this for a while also; an almost 50% regression > > > > is seen for single-process reads (ie sync) if slice_idle is 1ms or > > > > more (eg default of 8) [1], which seems phenomenal. > > > > > > > > Jens, is this the expected price to pay for optimal busy-spindle > > > > scheduling, a design issue, bug or am I missing something totally? > > > > > > > > Thanks, > > > > Daniel > [snip] > ... > [snip] > > > > > > Thisd would appear to be quite a considerable performance difference. > > > > Indeed, that is of course a bug. The initial mail here mentions this as > > a regression - which kernel was the last that worked ok? > > > > If someone would send me a blktrace of such a slow run, that would be > > nice. Basically just do a blktrace /dev/sda (or whatever device) while > > doing the hdparm, preferably storing output files on a difference > > device. Then send the raw sda.blktrace.* files to me. Thanks! > > > > -- > > Jens Axboe > > > > > > Hi Jens, > > I called this a "regression" since I wasn't sure if this is a real bug > or just something introduced recently, I just started to use cfq as > main io-scheduler so I can't tell ... > > testing 2.6.17 unfortunately is somewhat impossible for me (reiser4; > too new hardware - problems with jmicron) > > google "says" that it seemingly already existed since at least 2.6.18 > (Ubuntu DapperDrake) [see: > http://ubuntuforums.org/showpost.php?p=1484633&postcount=12]
Funky :/
> well - back to topic: > > for a blktrace one need to enable CONFIG_BLK_DEV_IO_TRACE , right ? > blktrace can be obtained from your git-repo ?
Yes on both accounts, or just grab a blktrace snapshot from:
http://brick.kernel.dk/snaps/blktrace-git-latest.tar.gz
if you don't use git.
-- Jens Axboe
| |