> On Mar 23, 2021, at 9:21 AM, Namhyung Kim <namhy...@kernel.org> wrote:
>
> As we can run many jobs (in container) on a big machine, we want to
> measure each job's performance during the run. To do that, the
> perf_event can be associated to a cgroup to measure it only.
>
> However such cgroup events need to be opened separately and it causes
> significant overhead in event multiplexing during the context switch
> as well as resource consumption like in file descriptors and memory
> footprint.
>
> As a cgroup event is basically a cpu event, we can share a single cpu
> event for multiple cgroups. All we need is a separate counter (and
> two timing variables) for each cgroup. I added a hash table to map
> from cgroup id to the attached cgroups.
>
> With this change, the cpu event needs to calculate a delta of event
> counter values when the cgroups of current and the next task are
> different. And it attributes the delta to the current task's cgroup.
>
> This patch adds two new ioctl commands to perf_event for light-weight
> cgroup event counting (i.e. perf stat).
>
> * PERF_EVENT_IOC_ATTACH_CGROUP - it takes a buffer consists of a
> 64-bit array to attach given cgroups. The first element is a
> number of cgroups in the buffer, and the rest is a list of cgroup
> ids to add a cgroup info to the given event.
>
> * PERF_EVENT_IOC_READ_CGROUP - it takes a buffer consists of a 64-bit
> array to get the event counter values. The first element is size
> of the array in byte, and the second element is a cgroup id to
> read. The rest is to save the counter value and timings.
>
> This attaches all cgroups in a single syscall and I didn't add the
> DETACH command deliberately to make the implementation simple. The
> attached cgroup nodes would be deleted when the file descriptor of the
> perf_event is closed.
This is very interesting idea!
Could you please add some description of the relationship among
perf_event and contexts? The code is a little confusing. For example,
why do we need cgroup_ctx_list?
Thanks,
Song
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