From: Shaohua Li <shaohua.li@intel.com>
To: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
x86@kernel.org
Subject: Re: [PATCH block:for-3.3/core] block: disable ELEVATOR_INSERT_SORT_MERGE
Date: Fri, 06 Jan 2012 12:19:05 +0800 [thread overview]
Message-ID: <1325823545.22361.526.camel@sli10-conroe> (raw)
In-Reply-To: <20120106035247.GF6276@google.com>
On Thu, 2012-01-05 at 19:52 -0800, Tejun Heo wrote:
> 5e84ea3a9c "block: attempt to merge with existing requests on plug
> flush" added support for merging requests on plug flush and 274193224c
> "block: recursive merge requests" added recursive merging.
>
> Because these mergings happen before the request is inserted on the
> elevator, the usual elv_latter/former_request() can't be used to
> locate merge candidates. It instead used bio merging mechanism -
> last_merge hint and rqhash; unfortunately, this means that the
> elevator doesn't have a say in which are allowed to merge and which
> aren't.
>
> For cfq, this resulted in merges across different cfqq's which led to
> crashes as requests jump between different cfqq's unexpectedly.
>
> Proper solution would be improving merge mechanism such that we can
> always query elevator to find out merge candidates and remove rqhash;
> however, the merge window is already upon us. Disable
> INSERT_SORT_MERGE for now.
>
> For detailed discussion of the bug:
>
> http://thread.gmane.org/gmane.linux.kernel.next/20064/focus=20159
>
this is overkill. when plug is added, we found huge performance
regression, that's why we add INSERT_SORT_MERGE.
Thanks,
Shaohua
next prev parent reply other threads:[~2012-01-06 4:19 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20111221174733.9ba0861e762e8d96844b060b@canb.auug.org.au>
2011-12-21 23:15 ` linux-next: Tree for Dec 21 Andrew Morton
2011-12-22 23:08 ` Andrew Morton
2011-12-22 23:20 ` Tejun Heo
2011-12-22 23:24 ` Andrew Morton
2011-12-22 23:38 ` Tejun Heo
2011-12-22 23:44 ` Andrew Morton
2011-12-22 23:46 ` Tejun Heo
2011-12-23 0:42 ` Tejun Heo
2011-12-24 5:13 ` Hugh Dickins
2011-12-25 1:02 ` [PATCH block/for-3.3/core] block: an exiting task should be allowed to create io_context Tejun Heo
2011-12-25 13:29 ` Jens Axboe
2011-12-27 22:07 ` Andrew Morton
2011-12-28 8:33 ` Hugh Dickins
2011-12-28 16:48 ` Tejun Heo
2011-12-28 17:50 ` Hugh Dickins
2011-12-28 17:55 ` Tejun Heo
2011-12-28 21:19 ` Tejun Heo
2012-01-03 17:35 ` Tejun Heo
2012-01-03 17:59 ` Tejun Heo
2012-01-03 20:09 ` Tejun Heo
2012-01-03 20:20 ` Jens Axboe
2012-01-03 22:13 ` Tejun Heo
2012-01-03 22:35 ` Tejun Heo
2012-01-05 1:24 ` Tejun Heo
2012-01-05 18:36 ` Hugh Dickins
2012-01-05 18:38 ` Tejun Heo
2012-01-06 2:17 ` [PATCH block:for-3.3/core] cfq: merged request shouldn't jump to a different cfqq Tejun Heo
2012-01-06 2:36 ` Tejun Heo
2012-01-06 3:14 ` Shaohua Li
2012-01-06 3:04 ` Tejun Heo
2012-01-06 3:30 ` Tejun Heo
2012-01-06 3:52 ` [PATCH block:for-3.3/core] block: disable ELEVATOR_INSERT_SORT_MERGE Tejun Heo
2012-01-06 4:19 ` Shaohua Li [this message]
2012-01-06 4:38 ` Tejun Heo
2012-01-06 8:15 ` Shaohua Li
2012-01-06 15:34 ` Tejun Heo
2012-01-06 3:34 ` [PATCH block:for-3.3/core] cfq: merged request shouldn't jump to a different cfqq Shaohua Li
2012-01-06 3:22 ` Tejun Heo
2012-01-06 4:15 ` Shaohua Li
2012-01-06 4:40 ` Tejun Heo
2012-01-06 2:47 ` Shaohua Li
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