Messages in this thread | | | Date | Thu, 11 May 2006 10:02:15 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 0/10] bulk cpu removal support |
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Ashok Raj <ashok.raj@intel.com> wrote: > > On Wed, May 10, 2006 at 11:06:06PM -0700, Andrew Morton wrote: > Hi Andrew, > > > Shaohua Li <shaohua.li@intel.com> wrote: > > > > > > CPU hotremove will migrate tasks and redirect interrupts off dead cpu. > > > > This seems an awful lot of code for something which happens so infrequently. > > > > How big is the problem you're fixing here, and what are the > > user-observeable effects of these changes? > > This is useful when say a NUMA node is being removed. With new multi-core > CPUs comming up, considering a 2 core with HT, we could have up to 4 logical > per socket. On NUMA node with 4 sockets, a node removal will mean we > do 16 single cpu offlines. Each time the process and interrupts could > end up on a CPU that might be removed just immediatly. > > The same is also useful for SMP Suspend/resume cases since the logical offline > is same here as well. > > Even thought the code changes seem a lot, most of it is just preparation of > functions ready to accept a cpumask_t instead of a single cpu like earlier. > The reason we split them to smaller chunks so the scope of change is well > understood with each patch. > > The major changes are > > - stop machine to run cpu offline functions on each cpu going offline > - prepare offline functions in offline path to take cpumask_t > - Some task migrate dead lock removal consideration that we ran into > during stress test. > > I know Shaohua ran tests for more than 20+ hrs with the patch, both on i386 > and x86_64. > > once we get some time deltas on a bigger machine it will help a lot. > Iam also trying to check with some OEM';s who have such large machines for > some data.. keep posted. >
OK, thanks. I'm a little surprised that this patch wasn't accompanied by a problem description, really. I mean, if a single CPU offlining takes three milliseconds then why bother?
I assume it must take much longer, else you wouldn't have written the code. Have you any ballpark numbers for how long it _does_ take?
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