From: Dexuan Cui Subject: RE: ext4: performance regression introduced by the cgroup writeback support Date: Thu, 24 Sep 2015 00:15:37 +0000 Message-ID: <08750e508f1643b2a2c0bb495c91d450@SIXPR30MB031.064d.mgd.msft.net> References: <20150923161359.GB25218@ret.masoncoding.com> <20150923185337.GK26647@mtj.duckdns.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT To: Tejun Heo , Chris Mason , Theodore Ts'o , Andreas Dilger , "linux-ext4@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Return-path: In-Reply-To: <20150923185337.GK26647@mtj.duckdns.org> Content-Language: en-US Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org > -----Original Message----- > From: Tejun Heo [mailto:htejun@gmail.com] On Behalf Of Tejun Heo > Sent: Thursday, September 24, 2015 2:54 > To: Chris Mason ; Dexuan Cui ; > Theodore Ts'o ; Andreas Dilger ; > linux-ext4@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux- > kernel@vger.kernel.org > Subject: Re: ext4: performance regression introduced by the cgroup writeback > support > > On Wed, Sep 23, 2015 at 12:13:59PM -0400, Chris Mason wrote: > > > The issue is: under high CPU and disk I/O pressure, *some* processes can > suffer from a very slow write speed (e.g., <1MB/s or even only 20KB/s), while > the normal write speed should be at least dozens of MB/s. > > So, I think I know what caused this regression. Separate wb domains > shouldn't have been enabled on traditional hierarchies. It doesn't > work there and leads to multiple wb domains competing on the same > blkcg and the bw estimation would go completely haywire. Will update > soon. > > Thanks. > > -- > tejun Thanks a lot for the quick fix, Tejun! I'll test the fix. I'll report back in case it can't fix the issue --I think this is unlikely. :-) -- Dexuan