Messages in this thread | | | Date | Fri, 28 Jun 2013 21:31:52 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] block: Reserve only one queue tag for sync IO if only 3 tags are available |
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On Fri, Jun 28 2013, Jan Kara wrote: > In case a device has three tags available we still reserve two of them > for sync IO. That leaves only a single tag for async IO such as > writeback from flusher thread which results in poor performance. > > Allow async IO to consume two tags in case queue has three tag availabe > to get a decent async write performance. > > This patch improves streaming write performance on a machine with such disk > from ~21 MB/s to ~52 MB/s. Also postmark throughput in presence of > streaming writer improves from 8 to 12 transactions per second so sync > IO doesn't seem to be harmed in presence of heavy async writer.
That's pretty crazy! Never seen a device like that. But yes, it obviously exists, and the 2 reserved tags doesn't work well for that. So it's an improvement.
Thanks, will queue up for 3.11.
-- Jens Axboe
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