From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp02.au.ibm.com (e23smtp02.au.ibm.com [202.81.31.144]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e23smtp02.au.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id E74A82C0089 for ; Sat, 9 Feb 2013 05:12:01 +1100 (EST) Received: from /spool/local by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 9 Feb 2013 04:06:15 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 829D93578050 for ; Sat, 9 Feb 2013 05:11:58 +1100 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r18IBvBW6357300 for ; Sat, 9 Feb 2013 05:11:57 +1100 Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r18IBuZZ015688 for ; Sat, 9 Feb 2013 05:11:57 +1100 Message-ID: <51153F72.1060005@linux.vnet.ibm.com> Date: Fri, 08 Feb 2013 23:39:54 +0530 From: "Srivatsa S. Bhat" MIME-Version: 1.0 To: Russell King - ARM Linux Subject: Re: [PATCH v5 00/45] CPU hotplug: stop_machine()-free CPU hotplug References: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> <510FBC01.2030405@linux.vnet.ibm.com> <87haloiwv0.fsf@rustcorp.com.au> <51134596.4080106@linux.vnet.ibm.com> <20130208154113.GV17833@n2100.arm.linux.org.uk> <51152B81.2050501@linux.vnet.ibm.com> In-Reply-To: <51152B81.2050501@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-doc@vger.kernel.org, peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org, walken@google.com, mingo@kernel.org, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, xiaoguangrong@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, Rusty Russell , rostedt@goodmis.org, rjw@sisk.pl, namhyung@kernel.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, oleg@redhat.com, sbw@mit.edu, tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 02/08/2013 10:14 PM, Srivatsa S. Bhat wrote: > On 02/08/2013 09:11 PM, Russell King - ARM Linux wrote: >> On Thu, Feb 07, 2013 at 11:41:34AM +0530, Srivatsa S. Bhat wrote: >>> On 02/07/2013 09:44 AM, Rusty Russell wrote: >>>> "Srivatsa S. Bhat" writes: >>>>> On 01/22/2013 01:03 PM, Srivatsa S. Bhat wrote: >>>>> Avg. latency of 1 CPU offline (ms) [stop-cpu/stop-m/c latency] >>>>> >>>>> # online CPUs Mainline (with stop-m/c) This patchset (no stop-m/c) >>>>> >>>>> 8 17.04 7.73 >>>>> >>>>> 16 18.05 6.44 >>>>> >>>>> 32 17.31 7.39 >>>>> >>>>> 64 32.40 9.28 >>>>> >>>>> 128 98.23 7.35 >>>> >>>> Nice! >>> >>> Thank you :-) >>> >>>> I wonder how the ARM guys feel with their quad-cpu systems... >>>> >>> >>> That would be definitely interesting to know :-) >> >> That depends what exactly you'd like tested (and how) and whether you'd >> like it to be a test-chip based quad core, or an OMAP dual-core SoC. >> > > The effect of stop_machine() doesn't really depend on the CPU architecture > used underneath or the platform. It depends only on the _number_ of > _logical_ CPUs used. > > And stop_machine() has 2 noticeable drawbacks: > 1. It makes the hotplug operation itself slow > 2. and it causes disruptions to the workloads running on the other > CPUs by hijacking the entire machine for significant amounts of time. > > In my experiments (mentioned above), I tried to measure how my patchset > improves (reduces) the duration of hotplug (CPU offline) itself. Which is > also slightly indicative of the impact it has on the rest of the system. > > But what would be nice to test, is a setup where the workloads running on > the rest of the system are latency-sensitive, and measure the impact of > CPU offline on them, with this patchset applied. That would tell us how > far is this useful in making CPU hotplug less disruptive on the system. > > Of course, it would be nice to also see whether we observe any reduction > in hotplug duration itself (point 1 above) on ARM platforms with lot > of CPUs. [This could potentially speed up suspend/resume, which is used > rather heavily on ARM platforms]. > > The benefits from this patchset over mainline (both in terms of points > 1 and 2 above) is expected to increase, with increasing number of CPUs in > the system. > Adding Vincent to CC, who had previously evaluated the performance and latency implications of CPU hotplug on ARM platforms, IIRC. Regards, Srivatsa S. Bhat