Messages in this thread | | | Date | Mon, 19 Jan 2009 19:23:37 +0100 | From | Jens Axboe <> | Subject | Re: [RFC PATCH] block: Fix bio merge induced high I/O latency |
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On Mon, Jan 19 2009, Nikanth K wrote: > On Sun, Jan 18, 2009 at 12:34 AM, Jens Axboe <jens.axboe@oracle.com> wrote: > > > > > As a quick test, could you try and increase the slice_idle to eg 20ms? > > Sometimes I've seen timing being slightly off, which makes us miss the > > sync window for the ls (in your case) process. Then you get a mix of > > async and sync IO all the time, which very much slows down the sync > > process. > > > > Do you mean to say that 'ls' could not submit another request until > the previous sync request completes, but its idle window gets disabled > as it takes way too long to complete during heavy load? But when there
'ls' would never submit a new request before the previous one completes, such is the nature of sync processes. That's the whole reason we have the idle window.
> are requests in the driver, wont the idling be disabled anyway? Or did > you mean to increase slice_sync?
No, idling is on a per-cfqq (process) basis. I did not mean to increase slice_sync, that wont help at all. It's the window between submissions of requests that I wanted to test being larger, but apparently that wasn't the case here.
-- Jens Axboe
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