[lkml]   [2010]   [Jul]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 0/6 v6][RFC] jbd[2]: enhance fsync performance when using CFQ
Vivek Goyal <> writes:

> On Fri, Jul 02, 2010 at 03:58:13PM -0400, Jeff Moyer wrote:
> [..]
>> Changes from the last posting:
>> - Yielding no longer expires the current queue. Instead, it sets up new
>> requests from the target process so that they are issued in the yielding
>> process' cfqq. This means that we don't need to worry about losing group
>> or workload share.
>> - Journal commits are now synchronous I/Os, which was required to get any
>> sort of performance out of the fs_mark process in the presence of a
>> competing reader.
>> - WRITE_SYNC I/O no longer sets RQ_NOIDLE, for a similar reason.
> Hi Jeff,
> So this patchset relies on idling on WRITE_SYNC queues. Though in general
> we don't have examples that why one should idle on processes doing WRITE_SYNC
> IO because previous IO does not tell anything about the upcoming IO. I am
> bringing up this point again to make sure that fundamentally we agree that
> continue to idle on WRITE_SYNC is the right thing to do otherwise this patch
> will fall apart.

I think a mail server would be an example of an application that might
do this. I'll see if I can get a real world test case (or perhaps some
real world data) and verify that.

I agree that if we choose not to idle on write's, then this approach can
be thrown out the window.

> I have yet to go through the patch in detail but allowing other queue to
> dispatch requests in the same queue sounds like queue merging. So can
> we use that semantics to say elv_merge_context() or elv_merge_queue()
> instead of elv_yield(). In the code we can just merge the two queues when
> the next request comes in and separate them out at the slice expiry I
> guess.

I considered that approach, but then you run into all of the questions
about losing fairness across workloads and across groups. I believe the
approach I've taken here is *significantly* simpler than merging and
unmerging would be.


 \ /
  Last update: 2010-07-02 22:35    [W:0.038 / U:85.108 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site