Messages in this thread | | | Date | Wed, 9 May 2012 13:02:30 +0200 | Subject | Re: [PATCH 07/41] cpuset: Set up interface for nohz flag | From | Frederic Weisbecker <> |
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2012/5/9 Mike Galbraith <efault@gmx.de>: > On Tue, 2012-05-08 at 15:45 -0500, Christoph Lameter wrote: >> On Tue, 8 May 2012, Mike Galbraith wrote: >> >> > On Tue, 2012-05-08 at 18:16 +0200, Peter Zijlstra wrote: >> > > On Tue, 2012-05-08 at 10:57 -0500, Christoph Lameter wrote: >> > >> > > isolcpus is a very limited hack that adds more pain that its worth. Its >> > > yet another mask to check and its functionality is completely available >> > > through cpusets. >> > >> > Agreed. >> >> How would that work? By creating cpusets that only have a single cpu in >> them? > > No, just turn load balancing off for exclusive set, domains go poof.
I don't think it's
>> > > You cannot cree multi-cpu partitions using isolcpus, you cannot >> > > dynamically reconfigure it. >> > >> > Big plus for cpusets. >> >> Why would you want to do anything like it? cpusets are confusing. You can >> have a cpu be part of multiple cpusets. Which nohz setting applies for a >> particular cpu then? If any of the cpusets have nohz set then it applies >> to the cpu? And thus someone in a cpuset that does not has nohz set will >> find that a cpu will have nohz functionality? > > nohz has to be at least an exclusive set property. > >> Its not a good match for this. You would want a per cpu attribute for >> nohz. > > Or per cpuset, which can be the same thing as per cpu if you want. > >> > > And on the scheduler side cpusets doesn't add runtime overhead to normal >> > > things, only sched_setaffinity() and a few other rare operations get >> > > slightly more expensive. And it allows to reduce runtime overhead by >> > > making the load-balancer domains smaller. >> > >> > Very big deal if you have a load that doesn't do all the performance 'i' >> > dotting and 't' crossing it maybe could have, but ends up on a big box. >> >> isolcpus are not part of load balancer domains. > > Yup, so if you have an application with an RT component, somewhat > sensitive, needs isolation from rest of a big box, but app also has > SCHED_OTHER components. isolcpus is a pain, everything has to be static > and nailed to the floor. Load just works when plugged into a cpuset. > > -Mike > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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