From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Thornber Subject: Re: [PATCH 1/2] dm-kcopyd: introduce per-module throttle structure Date: Mon, 13 Jun 2011 10:17:16 +0100 Message-ID: <20110613091716.GC4580@ubuntu> References: <20110601095106.GA3718@ubuntu> <20110603110111.GA4969@ubuntu> <20110609094746.GA3152@ubuntu> <20110610084424.GA3672@ubuntu> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mikulas Patocka Cc: device-mapper development , "Alasdair G. Kergon" List-Id: dm-devel.ids On Sat, Jun 11, 2011 at 04:27:02PM -0400, Mikulas Patocka wrote: > It is much easier to explain to the users "if you set X value in > /sys/module/dm_mirror/parameters/raid1_resync_throttle, then the copying > will be done in X% of time, leaving the disk idle 100-X% of time", then to > invent some magic mechanisms that change multiple things based on X and > other conditions. Yes, that is very easy to explain to the users. This sort of description is what I was after when I kept asking you to tell me how to set it. It's not clear to me that setting the throttle to 80% will copy at 80% of the speed, or leave the disk idle for 20% of the time. Perhaps you have some benchmarks to back this up? (with different memory pressure situations please). Restricting the cpu available to issue io is not a great way to throttle io. There will be plenty of situations where 20% of the cpu is enough to swamp the devices. - Joe