From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dan Williams" Subject: Re: [PATCH 00/19] Hardware Accelerated MD RAID5: Introduction Date: Wed, 13 Sep 2006 12:17:55 -0700 Message-ID: References: <1158015632.4241.31.camel@dwillia2-linux.ch.intel.com> <20060913071512.GA23492@unthought.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20060913071512.GA23492@unthought.net> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Jakob Oestergaard , Dan Williams , NeilBrown , linux-raid@vger.kernel.org, akpm@osdl.org, linux-kernel@vger.kernel.org, christopher.leech@intel.com List-Id: linux-raid.ids On 9/13/06, Jakob Oestergaard wrote: > On Mon, Sep 11, 2006 at 04:00:32PM -0700, Dan Williams wrote: > > Neil, > > > ... > > > > Concerning the context switching performance concerns raised at the > > previous release, I have observed the following. For the hardware > > accelerated case it appears that performance is always better with the > > work queue than without since it allows multiple stripes to be operated > > on simultaneously. I expect the same for an SMP platform, but so far my > > testing has been limited to IOPs. For a single-processor > > non-accelerated configuration I have not observed performance > > degradation with work queue support enabled, but in the Kconfig option > > help text I recommend disabling it (CONFIG_MD_RAID456_WORKQUEUE). > > Out of curiosity; how does accelerated compare to non-accelerated? One quick example: 4-disk SATA array rebuild on iop321 without acceleration - 'top' reports md0_resync and md0_raid5 dueling for the CPU each at ~50% utilization. With acceleration - 'top' reports md0_resync cpu utilization at ~90% with the rest split between md0_raid5 and md0_raid5_ops. The sync speed reported by /proc/mdstat is ~40% higher in the accelerated case. That being said, array resync is a special case, so your mileage may vary with other applications. I will put together some data from bonnie++, iozone, maybe contest, and post it on SourceForge. > / jakob Dan