Messages in this thread |  | | | From | Jeff Moyer <> | | Subject | Re: [PATCH 2/2] cfq: allow dispatching of both sync and async I/O together | | Date | Mon, 21 Jun 2010 16:05:34 -0400 |
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Jens Axboe <axboe@kernel.dk> writes:
> On 21/06/10 21.49, Jeff Moyer wrote: >> Hi, >> >> In testing a workload that has a single fsync-ing process and another >> process that does a sequential buffered read, I was unable to tune CFQ >> to reach the throughput of deadline. This patch, along with the previous >> one, brought CFQ in line with deadline when setting slice_idle to 0. >> >> I'm not sure what the original reason for not allowing sync and async >> I/O to be dispatched together was. If there is a workload I should be >> testing that shows the inherent problems of this, please point me at it >> and I will resume testing. Until and unless that workload is identified, >> please consider applying this patch. > > The problematic case is/was a normal SATA drive with a buffered > writer and an occasional reader. I'll have to double check my > mail tomorrow, but iirc the issue was that the occasional reader > would suffer great latencies since service times for that single > IO would be delayed at the drive side. It could perhaps just be > a bug in how we handle the slice idling on the read side when the > IO gets delayed initially. > > So if my memory is correct, google for the fsync madness and > interactiveness thread that we had some months ago and which > caused a lot of tweaking. The commit adding this is > 5ad531db6e0f3c3c985666e83d3c1c4d53acccf9 and was added back > in July last year. So it was around that time that the mails went > around.
OK. Thanks a ton for the pointers! I really appreciate it!
-Jeff
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