Re: [RFC PATCH v4 00/19] Core scheduling v4

Aubrey Li
2020-02-25T05:38:32Z

On Tue, Feb 25, 2020 at 11:44 AM Aaron Lu <aaron.lwe@gmail.com> wrote:
>
> On Fri, Feb 14, 2020 at 02:10:53PM +0800, Aubrey Li wrote:
> > On Fri, Feb 14, 2020 at 2:37 AM Tim Chen <tim.c.chen@linux.intel.com> wrote:
> > >
> > > On 2/12/20 3:07 PM, Julien Desfossez wrote:
> > >
> > > >>
> > > >> Have you guys been able to make progress on the issues with I/O intensive workload?
> > > >
> > > > I finally have some results with the following branch:
> > > > https://github.com/digitalocean/linux-coresched/tree/coresched/v4-v5.5.y
> > > >
> > > >
> > > > So the main conclusion is that for all the test cases we have studied,
> > > > core scheduling performs better than nosmt ! This is different than what
> > > > we tested a while back, so it's looking really good !
> > >
> > > Thanks for the data. They look really encouraging.
> > >
> > > Aubrey is working on updating his patches so it will load balance
> > > to the idle cores a bit better. We are testing those and will post
> > > the update soon.
> >
> > I added a helper to check task and cpu cookie match, including the
> > entire core idle case. The refined patchset updated at here:
> > https://github.com/aubreyli/linux/tree/coresched_v4-v5.5.2
> >
> > This branch also includes Tim's patchset. According to our testing
> > result, the performance data looks on par with the previous version.
> > A good news is, v5.4.y stability issue on our 8 numa node machine
> > is gone on this v5.5.2 branch.
>
> One problem I have when testing this branch: the weight of the croup
> seems to be ignored.
>
> 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)
> most of the time since it has way more weight than cgB, while cgB should
> occupy almost no CPUs since:
> - when cgB's task is in the same CPU queue as cgA's task, then cgB's
> task is given very little CPU due to its small weight;
> - when cgB's task is in a CPU queue whose sibling's queue has cgA's
> task, cgB's task should be forced idle(again, due to its small weight).
>
> But testing shows cgA occupies only 2 cpus during the entire run while
> cgB enjoys the remaining 14 cpus. As a comparison, when coresched is off,
> cgA can occupy 8 cpus during its run.
>
> I haven't taken a look at the patches, but would like to raise the
> problem first. My gut feeling is that, we didn't make the CPU's load
> balanced.
>
> P.S. it's not that I care about VM's performance, it's just easier to
> test kernel stuff using a VM than on a bare metal. Its CPU setup might
> seem weird, I just set it up to be the same as my host setup.

Aaron - did you test this before? In other words, if you reset repo to your
last commit:

- 5bd3c80 sched/fair : Wake up forced idle siblings if needed

Does the problem remain? Just want to check if this is a regression
introduced by the subsequent patchset.

Thanks,
-Aubrey