linux-kernel - Re: [PATCH v5 0/5] dirty_log_perf

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Date:   Fri, 14 Oct 2022 09:55:27 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     "Wang, Wei W" <wei.w.wang@...el.com>,
        Vipin Sharma <vipinsh@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "andrew.jones@...ux.dev" <andrew.jones@...ux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 0/5] dirty_log_perf_test vCPU pinning

On Fri, Oct 14, 2022 at 9:34 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Fri, Oct 14, 2022, Wang, Wei W wrote:
> > On Tuesday, October 11, 2022 6:06 AM, Vipin Sharma wrote:
> > > Pin vCPUs to a host physical CPUs (pCPUs) in dirty_log_perf_test and optionally
> > > pin the main application thread to a physical cpu if provided. All tests based on
> > > perf_test_util framework can take advantage of it if needed.
> > >
> > > While at it, I changed atoi() to atoi_paranoid(), atoi_positive,
> > > atoi_non_negative() in other tests, sorted command line options alphabetically
> > > in dirty_log_perf_test, and added break between -e and -g which was missed in
> > > original commit when -e was introduced.
> >
> > Just curious why not re-using the existing tools (e.g. taskset) to do the pinning?
>
> IIUC, you're suggesting the test give tasks meaningful names so that the user can
> do taskset on the appropriate tasks?  The goal is to ensure vCPUs are pinned before
> they do any meaningful work.  I don't see how that can be accomplished with taskset
> without some form of hook in the test to effectively pause the test until the user
> (or some run script) is ready to continue.

A taskset approach would also be more difficult to incorporate into
automated runs of dirty_log_perf_test.

>
> Pinning aside, naming the threads is a great idea!  That would definitely help
> debug, e.g. if one vCPU gets stuck or is lagging behind.

+1

>
> >
> > For example, with below changes:
> > diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/se                                                                                                             lftests/kvm/lib/perf_test_util.c
> > index 9618b37c66f7..aac58d1acb3c 100644
> > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > @@ -264,6 +264,7 @@ void perf_test_start_vcpu_threads(int nr_vcpus,
> >                                   void (*vcpu_fn)(struct perf_test_vcpu_args *))
> >  {
> >         int i;
> > +       char vcpu_name[5];
> >
> >         vcpu_thread_fn = vcpu_fn;
> >         WRITE_ONCE(all_vcpu_threads_running, false);
> > @@ -275,6 +276,8 @@ void perf_test_start_vcpu_threads(int nr_vcpus,
> >                 WRITE_ONCE(vcpu->running, false);
> >
> >                 pthread_create(&vcpu->thread, NULL, vcpu_thread_main, vcpu);
> > +               sprintf(vcpu_name, "%s%d", "vcpu", i);
> > +               pthread_setname_np(vcpu->thread, vcpu_name);
> >         }
> >
> > and with top we can get
> >     PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
> >    4464 root      20   0 4248684   4.0g   1628 R  99.9  26.2   0:50.97 dirty_log_perf_
> >    4467 root      20   0 4248684   4.0g   1628 R  99.9  26.2   0:50.93 vcpu0
> >    4469 root      20   0 4248684   4.0g   1628 R  99.9  26.2   0:50.93 vcpu2
> >    4470 root      20   0 4248684   4.0g   1628 R  99.9  26.2   0:50.94 vcpu3
> >    4468 root      20   0 4248684   4.0g   1628 R  99.7  26.2   0:50.93 vcpu1