From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 21 May 2004 19:16:09 -0700 From: Andrew Morton Subject: Re: Slab cache reap and CPU availability Message-Id: <20040521191609.6f4a49a7.akpm@osdl.org> In-Reply-To: <200405211541.i4LFfpar001544@fsgi142.americas.sgi.com> References: <200405211541.i4LFfpar001544@fsgi142.americas.sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dimitri Sivanich Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Dimitri Sivanich wrote: > > Hi all, > > I have a fairly general question about the slab cache reap code. > > In running realtime noise tests on the 2.6 kernels (spinning to detect periods > of CPU unavailability to RT threads) on an IA/64 Altix system, I have found the > cache_reap code to be the source of a number of larger holdoffs (periods of > CPU unavailability). These can last into the 100's of usec on 1300 MHz CPUs. > Since this code runs periodically every few seconds as a timer softirq on all > CPUs, holdoffs can occur frequently. > > Has anyone looked into less interruptive alternatives to running cache_reap > this way (for the 2.6 kernel), or maybe looked into potential optimizations > to the routine itself? > Do you have stack backtraces? I thought the problem was via the RCU softirq callbacks, not via the timer interrupt. Dipankar spent some time looking at the RCU-related problem but solutions are not comfortable. What workload is triggering this? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org