On Tue, Jul 05, 2005 at 10:00:24AM -0400, Chris Mason wrote: > On Friday 01 July 2005 03:56, Suparna Bhattacharya wrote: > > Has anyone else noticed major throughput regressions for random > > reads/writes with aio-stress in 2.6.12 ? > > Or have there been any other FS/IO regressions lately ? > > > > On one test system I see a degradation from around 17+ MB/s to 11MB/s > > for random O_DIRECT AIO (aio-stress -o3 testext3/rwfile5) from 2.6.11 > > to 2.6.12. It doesn't seem filesystem specific. Not good :( > > > > BTW, Chris/Ben, it doesn't look like the changes to aio.c have had an > > impact (I copied those back to my 2.6.11 tree and tried the runs with no > > effect) So it is something else ... > > > > Ideas/thoughts/observations ? > > Lets try to narrow it down a bit: > > aio-stress -o 3 -d 1 will set the depth to 1, (io_submit then wait one > request This doesn't regress - the problem really happens when we don't wait one at a time.
> at a time). This doesn't take the aio subsystem out of the picture, but it > does make the block layer interaction more or less the same as non-aio > benchmarks. If this is slow, I would suspect something in the block layer, > and iozone -I -i 2 -w -f testext3/rwfile5 should also show the regression. > > If it doesn't regress, I would suspect something in the aio core. My first > attempts at the context switch reduction patches caused this kind of > regression. There was too much latency in sending the events up to userland. > > Other options: > > Try different elevators Still regresses (I tried noop instead of as) > Try O_SYNC aio random writes > Try aio random reads > Try buffers random reads Again all these end up waiting one at a time with mainline because it forces buffered AIO to be synchronous, so we the regression doesn't show up. But, when I apply my patches to make buffered fsAIO async, so we aren't waiting one at a time -- there is a similar regression. In fact it was this regression that made me go back and check if it was happening with AIO-DIO as well. Regards Suparna > > -chris -- Suparna Bhattacharya ([EMAIL PROTECTED]) Linux Technology Center IBM Software Lab, India - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
