Messages in this thread | | | Subject | Re: [PATCH 0/2] cpusets,isolcpus: resolve conflict between cpusets and isolcpus | From | Mike Galbraith <> | Date | Tue, 24 Feb 2015 15:22:16 +0100 |
| |
On Tue, 2015-02-24 at 09:13 -0500, Rik van Riel wrote: > On 02/23/2015 09:18 PM, Mike Galbraith wrote: > > On Mon, 2015-02-23 at 16:45 -0500, riel@redhat.com wrote: > >> Ensure that cpus specified with the isolcpus= boot commandline > >> option stay outside of the load balancing in the kernel > >> scheduler. > >> > >> Operations like load balancing can introduce unwanted latencies, > >> which is exactly what the isolcpus= commandline is there to > >> prevent. > >> > >> Previously, simply creating a new cpuset, without even touching > >> the cpuset.cpus field inside the new cpuset, would undo the > >> effects of isolcpus=, by creating a scheduler domain spanning the > >> whole system, and setting up load balancing inside that domain. > >> The cpuset root cpuset.cpus file is read-only, so there was not > >> even a way to undo that effect. > >> > >> This does not impact the majority of cpusets users, since > >> isolcpus= is a fairly specialized feature used for realtime > >> purposes. > > > > 3/3: nohz_full cpus become part of that unified isolated map? > > There may be use cases where users want nohz_full, but still > want the scheduler to automatically load balance the CPU. > > I am not sure whether we want nohz_full and isolcpus to always > overlap 100%. > > On the other hand, any CPU that is isolated with isolcpus= > probably wants nohz_full...
I can't imagine caring deeply about the tiny interference of the tick, yet not caring about the massive interference of load balancing.
-Mike
| |