lkml.org 
[lkml]   [2008]   [Oct]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority
Date
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.




\
 
 \ /
  Last update: 2008-10-02 17:25    [W:0.065 / U:0.832 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site