Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH 1/2] perf/core: Share an event with multiple cgroups | Date | Wed, 24 Mar 2021 00:30:05 +0000 |
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> On Mar 23, 2021, at 9:21 AM, Namhyung Kim <namhyung@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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