linux-kernel - Re: [PATCH v4 0/3] perf: add support for analyzing events for containers

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Date:   Fri, 16 Dec 2016 13:14:01 +0100
From:   Alban Crequy <alban.crequy@...il.com>
To:     Hari Bathini <hbathini@...ux.vnet.ibm.com>
Cc:     ananth@...ibm.com, daniel@...earbox.net,
        Linux Containers <containers@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        mingo@...hat.com, paulus@...ba.org, rostedt@...dmis.org,
        aravinda@...ux.vnet.ibm.com, kernel@...p.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v4 0/3] perf: add support for analyzing events for containers

Hi,

> Currently, there is no trivial mechanism to analyze events based on
> containers. perf -G can be used, but it will not filter events for the
> containers created after perf is invoked, making it difficult to assess/
> analyze performance issues of multiple containers at once.
>
> This patch-set overcomes this limitation by using cgroup identifier as
> container unique identifier. A new PERF_RECORD_NAMESPACES event that
> records namespaces related info is introduced, from which the cgroup
> namespace's device & inode numbers are used as cgroup identifier. This
> is based on the assumption that each container is created with it's own
> cgroup namespace allowing assessment/analysis of multiple containers
> using cgroup identifier.
>
> The first patch introduces PERF_RECORD_NAMESPACES in kernel while the
> second patch makes the corresponding changes in perf tool to read this
> PERF_RECORD_NAMESPACES events. The third patch adds a cgroup identifier
> column in perf report, which contains the cgroup namespace's device and
> inode numbers.

I have a question for the pid namespace: does the new perf event gives
the pid namespace of the task, or the pid_ns_for_children from the
nsproxy? From my limited understanding, v4 seems to do the former, as
opposed to v3.

When synthesizing events from /proc/$PID/ns/pid, it cannot take the
pid_ns_for_children, so I wanted to make sure it is consistent.

Cheers,
Alban