Messages in this thread | | | Date | Tue, 27 Feb 2007 10:42:11 +0100 | From | Jens Axboe <> | Subject | Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3) |
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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?
> 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 not take advantage of queueing. How does the job file perform with ioengine=sync?
> 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.
-- Jens Axboe
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