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

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Message-Id: <40b222dc-5149-4f82-4d5e-6a8d188a6a35@linux.vnet.ibm.com>
Date:   Tue, 3 Jan 2017 16:57:54 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     ast@...com, peterz@...radead.org,
        lkml <linux-kernel@...r.kernel.org>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, mingo@...hat.com,
        daniel@...earbox.net, rostedt@...dmis.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        ebiederm@...ssion.com, sargun@...gun.me,
        Aravinda Prasad <aravinda@...ux.vnet.ibm.com>,
        brendan.d.gregg@...il.com
Subject: Re: [PATCH v4 0/3] perf: add support for analyzing events for
 containers

Hi Krister,

Thanks for reviewing..


On Thursday 29 December 2016 07:11 AM, Krister Johansen wrote:
> On Fri, Dec 16, 2016 at 12:06:55AM +0530, Hari Bathini wrote:
>> 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.
> Why choose cgroups when the kernel dispenses namespace-unique
> identifiers. Cgroup membership can be arbitrary.  Moreover, cgroup and

Agreed. But doesn't that hold for any other namespace or a combination
of namespaces as well?

> namespace destruction are handled by separate subsystems.  It's possible
> to have a cgroup notifier run prior to network namespace teardown
> occurring.
> If it were me, I'd re-use existing convention to identify the namespaces
> you want to monitor.  The code in nsenter(1) can take a namespace that's
> been bind mount'd on a file, or extract the ns information from a task
> in /procfs.

As PERF_RECORD_NAMESPACES gets all namespaces info, I assume your 
reservation
is with how perf report (patch 3/3) is processed, which could be 
improved to consider
other namespaces as well, once PERF_RECORD_NAMESPACES is in.

> My biggest concern is how the sample data is handled after it has been
> collected.  Both namespaces and cgroups don't survive reboots.  Will the
> records will contain all the persistent state needed to run a report or
> script command at a later date?

Yes. Sideband events are emitted when a new thread is created or an existing
thread's namespaces are changed, which can be post processed for reporting.

> Does this code attempt to enter alternate namespaces in order to record
> stack/symbol information for a '-g' style trace?  If so, how are you
> holding on to that information?  There's no guarantee that a particular
> container will be alive or have its filesystems reachable from the host
> if the trace data is evaluated at a later time.

I am not altering the existing behavior of -g option with these patches..

Thanks
Hari