Messages in this thread | | | From | Bodo Eggert <> | Subject | Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority | Date | Thu, 02 Oct 2008 17:32:04 +0200 |
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Jens Axboe <jens.axboe@oracle.com> wrote: > On Thu, Oct 02 2008, Dave Chinner wrote: >> On Thu, Oct 02, 2008 at 09:55:11AM +0200, Jens Axboe wrote:
>> > Good point. I think we should mark the IO as sync, and maintain the same >> > priority level. Any IO that ends up being waited on is sync by >> > definition, we just need to expand the coverage a bit. >> >> That's what XFS has always done - mark the journal I/O as sync. >> Still, once you load up the elevator, the sync I/O can still get >> delayed for hundreds of milliseconds before dispatch, which was >> why I started looking at boosting the priority of the log I/O. >> It proved to be much more effective at getting the log I/O >> dispatched than the existing "mark it sync" technique.... > > Sure, just marking it as sync is not a magic bullet. It'll be in the > first priority for that class, but it'll share bandwidth with other > processes. So if you have lots of IO going on, it can take hundreds of > miliseconds before being dispatched.
Sounds like you need a priority class besides sync and async.
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