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Subject: Re: [PATCH v3] perf bench sched pipe: Add -G/--cgroups option
From:   Athira Rajeev <atrajeev@linux.vnet.ibm.com>
In-Reply-To: <ZS1Y5PhXhp384ynY@kernel.org>
Date:   Tue, 17 Oct 2023 13:36:49 +0530
Cc:     Ingo Molnar <mingo@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-perf-users <linux-perf-users@vger.kernel.org>
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Message-Id: <D6B30B31-80DC-4EB0-A111-B92CD99DD75F@linux.vnet.ibm.com>
References: <20231016044225.1125674-1-namhyung@kernel.org>
 <ZS0D53ckVx356k4o@gmail.com> <ZS1Y5PhXhp384ynY@kernel.org>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>
Precedence: bulk


> On 16-Oct-2023, at 9:08 PM, Arnaldo Carvalho de Melo <acme@kernel.org> =
wrote:
>=20
> Em Mon, Oct 16, 2023 at 11:35:35AM +0200, Ingo Molnar escreveu:
>>=20
>>=20
>> * Namhyung Kim <namhyung@kernel.org> wrote:
>>=20
>>> + /* try cgroup v2 interface first */
>>> + if (threaded)
>>> + fd =3D openat(cgrp->fd, "cgroup.threads", O_WRONLY);
>>> + else
>>> + fd =3D openat(cgrp->fd, "cgroup.procs", O_WRONLY);
>>> +
>>> + /* try cgroup v1 if failed */
>>> + if (fd < 0)
>>> + fd =3D openat(cgrp->fd, "tasks", O_WRONLY);
>>> +
>>> + if (fd < 0) {
>>> + char mnt[PATH_MAX];
>>> +
>>> + printf("Failed to open cgroup file in %s\n", cgrp->name);
>>> +
>>> + if (cgroupfs_find_mountpoint(mnt, sizeof(mnt), "perf_event") =3D=3D =
0)
>>> + printf(" Hint: create the cgroup first, like 'mkdir %s/%s'\n",
>>> +        mnt, cgrp->name);
>>=20
>> Ok, this works too I suppose.
>>=20
>> Acked-by: Ingo Molnar <mingo@kernel.org>
>=20
> I'm not getting that:
>=20
> [root@five ~]# perf bench sched pipe -l 10000 -G AAA,BBB
> # Running 'sched/pipe' benchmark:
> no access to cgroup /sys/fs/cgroup/AAA
> cannot open sender cgroup: AAA
> Usage: perf bench sched pipe <options>
>=20
>    -G, --cgroups <SEND,RECV>
>                          Put sender and receivers in given cgroups
> [root@five ~]#
>=20
> Its better now as it bails out, but it is not emitting any message =
that
> helps with running the test, well, there is that /sys/fs/cgroup/AAA
> path, lemme try doing a mkdir:
>=20
> [root@five ~]# perf bench sched pipe -l 10000 -G AAA,BBB
> # Running 'sched/pipe' benchmark:
> no access to cgroup /sys/fs/cgroup/BBB
> cannot open receiver cgroup: BBB
> Usage: perf bench sched pipe <options>
>=20
>    -G, --cgroups <SEND,RECV>
>                          Put sender and receivers in given cgroups
> [root@five ~]#
>=20
> [root@five ~]# perf bench sched pipe -l 10000 -G AAA,BBB
> # Running 'sched/pipe' benchmark:
> [root@five ~]#
>=20
> It seems to be bailing out but doesn't run the test nor emits any
> warning.

In the =E2=80=9Cparse_two_cgroups=E2=80=9D function itself it checks for =
:

cgrp_send =3D cgroup__new(p, /*do_open=3D*/true);
        if (cgrp_send =3D=3D NULL) {
                fprintf(stderr, "cannot open sender cgroup: %s", p);
                goto out;
        }

And we fail here since the cgroup is not created. May be we can add the =
Hint or warning in here ?


Thanks
Athira

>=20
> I'm using v3. I'll try to debug it a bit.
>=20
> - Arnaldo