Re: [PATCH v2] perf bench sched pipe: Add -G/--cgroups option

[Namhyung Kim]

On Sat, Oct 14, 2023 at 1:44 AM Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>
> * Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> > +     cgrp_send = cgroup__new(p, /*do_open=*/true);
> > +     if (cgrp_send == NULL) {
> > +             fprintf(stderr, "cannot open sender cgroup: %s", p);
> > +             goto out;
> > +     }
>
> Maybe in this case print out a small suggestion of how to create this
> particular cgroup?
>
> Most distro users and even kernel developers don't ever have to create
> new cgroups.
>
> Maybe even allow the creation of new cgroups for this testing, if they
> don't already exist? As long as we don't delete any cgroups I don't think
> much harm can be done - and the increase in usability is substantial.

I'm not sure if it's ok create a new cgroup and leave it after the use.
Anyway, none of the existing subcommands create new cgroups
IIUC and I think it'd be ok to print a message on how to create one.

>
> > +static void enter_cgroup(struct cgroup *cgrp)
> > +{
> > +     char buf[32];
> > +     int fd, len;
> > +     pid_t pid;
> > +
> > +     if (cgrp == NULL)
> > +             return;
> > +
> > +     if (threaded)
> > +             pid = syscall(__NR_gettid);
> > +     else
> > +             pid = getpid();
> > +
> > +     snprintf(buf, sizeof(buf), "%d\n", pid);
> > +     len = strlen(buf);
> > +
> > +     /* try cgroup v2 interface first */
> > +     if (threaded)
> > +             fd = openat(cgrp->fd, "cgroup.threads", O_WRONLY);
> > +     else
> > +             fd = openat(cgrp->fd, "cgroup.procs", O_WRONLY);
> > +
> > +     /* try cgroup v1 if failed */
> > +     if (fd < 0)
> > +             fd = openat(cgrp->fd, "tasks", O_WRONLY);
> > +
> > +     if (fd < 0) {
> > +             printf("failed to open cgroup file in %s\n", cgrp->name);
> > +             return;
> > +     }
> > +
> > +     if (write(fd, buf, len) != len)
> > +             printf("cannot enter to cgroup: %s\n", cgrp->name);
>
> The failures here should probably result in termination of the run with an
> error code, not just messages which are easy to skip in automated tests?

Right, I'll make the change.

Thanks,
Namhyung