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Message-ID: <20070227123932.GA8720@in.ibm.com> Date: Tue, 27 Feb 2007 18:09:32 +0530 From: Suparna Bhattacharya <suparna@...ibm.com> To: Jens Axboe <jens.axboe@...cle.com> Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Arjan van de Ven <arjan@...radead.org>, Christoph Hellwig <hch@...radead.org>, Andrew Morton <akpm@....com.au>, Alan Cox <alan@...rguk.ukuu.org.uk>, Ulrich Drepper <drepper@...hat.com>, Zach Brown <zach.brown@...cle.com>, Evgeniy Polyakov <johnpol@....mipt.ru>, "David S. Miller" <davem@...emloft.net>, Davide Libenzi <davidel@...ilserver.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3) On Tue, Feb 27, 2007 at 10:42:11AM +0100, Jens Axboe wrote: > On Tue, Feb 27 2007, Suparna Bhattacharya wrote: > > On Mon, Feb 26, 2007 at 03:45:48PM +0100, Jens Axboe wrote: > > > On Mon, Feb 26 2007, Suparna Bhattacharya wrote: > > > > On Mon, Feb 26, 2007 at 02:57:36PM +0100, Jens Axboe wrote: > > > > > > > > > > Some more results, using a larger number of processes and io depths. A > > > > > repeat of the tests from friday, with added depth 20000 for syslet and > > > > > libaio: > > > > > > > > > > Engine Depth Processes Bw (MiB/sec) > > > > > ---------------------------------------------------- > > > > > libaio 1 1 602 > > > > > syslet 1 1 759 > > > > > sync 1 1 776 > > > > > libaio 32 1 832 > > > > > syslet 32 1 898 > > > > > libaio 20000 1 581 > > > > > syslet 20000 1 609 > > > > > > > > > > syslet still on top. Measuring O_DIRECT reads (of 4kb size) on ramfs > > > > > with 100 processes each with a depth of 200, reading a per-process > > > > > private file of 10mb (need to fit in my ram...) 10 times each. IOW, > > > > > doing 10,000MiB of IO in total: > > > > > > > > But, why ramfs ? Don't we want to exercise the case where O_DIRECT actually > > > > blocks ? Or am I missing something here ? > > > > > > Just overhead numbers for that test case, lets try something like your > > > described job. > > > > > > Test case is doing random reads from /dev/sdb, in chunks of 64kb: > > > > > > Engine Depth Processes Bw (KiB/sec) > > > ---------------------------------------------------- > > > libaio 200 100 2813 > > > syslet 200 100 3944 > > > libaio 20000 1 2793 > > > syslet 20000 1 3854 > > > sync (*) 20000 1 2866 > > > > > > deadline was used for IO scheduling, to minimize impact. Not sure why > > > syslet actually does so much better here, looing at vmstat the rate is > > > steady and all runs are basically 50/50 idle/wait. One difference is > > > that the submission itself takes a long time on libaio, since the > > > io_submit() will block on request allocation. The generated IO pattern > > > from each process is the same for all runs. The drive is a lousy sata > > > that doesn't even do queuing, FWIW. > > > > > > I tried the latest fio code with syslet v4, and my results are a little > > different - have yet to figure out why or what to make of it. > > I hope I have all the right pieces now. > > > > This is an ext2 filesystem, SCSI AIC7xxx. > > > > I used an iodepth_batch size of 8 to limit the number of ios in a single > > io_submit (thanks for adding that parameter to fio !), like we did in > > aio-stress. > > > > Engine Depth Batch Bw (KiB/sec) > > ---------------------------------------------------- > > libaio 64 8 17,226 > > syslet 64 8 17,620 > > libaio 20000 8 18,552 > > syslet 20000 8 14,935 > > > > > > Which is not bad, actually. > > It's not bad for such a high depth/batch setting, but I still wonder why > are results are so different. I'll look around for an x86 box with some > TCQ/NCQ enabled storage attached for testing. Can you pass me your > command line or job file (whatever you use) so we are on the same page? Sure - I used variations of the following job file (e.g. engine=syslet-rw, iodepth=20000). Also the io scheduler on my system is set to Anticipatory by default. FWIW it is a 4 way SMP (PIII, 700MHz) ; aio-stress -l -O -o3 <1GB file> [global] ioengine=libaio buffered=0 rw=randread bs=64k size=1024m directory=/kdump/suparna [testfile2] iodepth=64 iodepth_batch=8 > > > If I do not specify the iodepth_batch (i.e. default to depth), then the > > difference becomes more pronounced at higher depths. However, I doubt > > whether anyone would be using such high batch sizes in practice ... > > > > Engine Depth Batch Bw (KiB/sec) > > ---------------------------------------------------- > > libaio 64 default 17,429 > > syslet 64 default 16,155 > > libaio 20000 default 15,494 > > syslet 20000 default 7,971 > > > If iodepth_batch isn't set, the syslet queued io will be serialized and I see, so then this particular setting is not very meaningful > not take advantage of queueing. How does the job file perform with > ioengine=sync? Just tried it now : 9,027KiB/s > > > Often times it is the application tuning that makes all the difference, > > so am not really sure how much to read into these results. > > That's always been the hard part of async io ... > > Yes I agree, it's handy to get an overview though. True, at least some of this helps us gain a little more understanding about the boundaries and how to tune it to be most effective. Regards Suparna > > -- > Jens Axboe -- Suparna Bhattacharya (suparna@...ibm.com) 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 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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