Messages in this thread | | | From | Aubrey Li <> | Date | Thu, 27 Feb 2020 22:37:20 +0800 | Subject | Re: [RFC PATCH v4 00/19] Core scheduling v4 |
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On Thu, Feb 27, 2020 at 10:10 PM Phil Auld <pauld@redhat.com> wrote: > > Hi Aaron, > > On Thu, Feb 27, 2020 at 10:04:32AM +0800 Aaron Lu wrote: > > On Tue, Feb 25, 2020 at 03:51:37PM -0500, Vineeth Remanan Pillai wrote: > > > On a 2sockets/16cores/32threads VM, I grouped 8 sysbench(cpu mode) > > > > threads into one cgroup(cgA) and another 16 sysbench(cpu mode) threads > > > > into another cgroup(cgB). cgA and cgB's cpusets are set to the same > > > > socket's 8 cores/16 CPUs and cgA's cpu.shares is set to 10240 while cgB's > > > > cpu.shares is set to 2(so consider cgB as noise workload and cgA as > > > > the real workload). > > > > > > > > I had expected cgA to occupy 8 cpus(with each cpu on a different core) > > > > > > The expected behaviour could also be that 8 processes share 4 cores and > > > 8 hw threads right? This is what we are seeing mostly > > > > I expect the 8 cgA tasks to spread on each core, instead of occupying > > 4 cores/8 hw threads. If they stay on 4 cores/8 hw threads, than on the > > core level, these cores' load would be much higher than other cores > > which are running cgB's tasks, this doesn't look right to me. > > > > I don't think that's a valid assumption, at least since the load balancer rework. > > The scheduler will be looking much more at the number of running task versus > the group weight. So in this case 2 running tasks, 2 siblings at the core level > will look fine. There will be no reason to migrate.
Can this be replicated?
> > > I think the end result should be: each core has two tasks queued, one > > cgA task and one cgB task(to maintain load balance on the core level). > > The two tasks are queued on different hw thread, with cgA's task runs > > most of the time on one thread and cgB's task being forced idle most > > of the time on the other thread. > > > > With the core scheduler that does not seem to be a desired outcome. I think > grouping the 8 cgA tasks on the 8 cpus of 4 cores seems right. > Especially, if the load of cgA task + cgB task > cpu capacity, grouping cgA tasks can avoid forced idle completely. Maintaining core level balance seems not the best result. I guess that's why with core scheduler enabled we saw 10-20% improvement in some cases against the default core scheduler disabled.
Thanks, -Aubrey
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