linux-kernel - Re: [PATCHSET] blk-throttle: implement proper hierarchy support

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Date:	Fri, 3 May 2013 11:57:51 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, lkml <linux-kernel@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCHSET] blk-throttle: implement proper hierarchy support

On Fri, May 03, 2013 at 01:56:52PM -0400, Vivek Goyal wrote:
> > Yeah, I think that's what *should* be happening but not what I'm
> > seeing.  I'm seeing ~15% penalty.
> 
> What test are you running. I am running a simple dd with directIO and
> I am not seeing any penalty.

Combination of dd and a test program that I've been using for some
while which can generate concurrent direct random IOs.  Attaching the
source code for the latter.

> # set limit to 1000000 bytes/second both in parent and child cgroup
> # dd if=/dev/vdb of=/dev/null iflag=direct
> 
> I will capture blktrace and analyze it though to understand better
> what's happening.

Try using larger block size.  It looks like dispatch windows being
reset depending on timing is hurting the overall bandwidth.  It
becomes pronounced with larger IOs.

Thanks.

-- 
tejun
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