Re: [PATCH v3] perf bench sched pipe: Add -G/--cgroups option

[Athira Rajeev]

> On 16-Oct-2023, at 9:08 PM, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> 
> Em Mon, Oct 16, 2023 at 11:35:35AM +0200, Ingo Molnar escreveu:
>> 
>> 
>> * Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>> 
>>> + /* 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) {
>>> + char mnt[PATH_MAX];
>>> +
>>> + printf("Failed to open cgroup file in %s\n", cgrp->name);
>>> +
>>> + if (cgroupfs_find_mountpoint(mnt, sizeof(mnt), "perf_event") == 0)
>>> + printf(" Hint: create the cgroup first, like 'mkdir %s/%s'\n",
>>> +        mnt, cgrp->name);
>> 
>> Ok, this works too I suppose.
>> 
>> Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
> 
> I'm not getting that:
> 
> [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>
> 
>    -G, --cgroups <SEND,RECV>
>                          Put sender and receivers in given cgroups
> [root@five ~]#
> 
> 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:
> 
> [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>
> 
>    -G, --cgroups <SEND,RECV>
>                          Put sender and receivers in given cgroups
> [root@five ~]#
> 
> [root@five ~]# perf bench sched pipe -l 10000 -G AAA,BBB
> # Running 'sched/pipe' benchmark:
> [root@five ~]#
> 
> It seems to be bailing out but doesn't run the test nor emits any
> warning.

In the “parse_two_cgroups” function itself it checks for :

cgrp_send = cgroup__new(p, /*do_open=*/true);
        if (cgrp_send == 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

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