linux-kernel - Re: [PATCH v2 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

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Date:   Fri, 9 Dec 2016 15:40:36 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     ast@...com, 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 v2 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info



On Friday 09 December 2016 12:10 AM, Hari Bathini wrote:
> Hi Peter,
>
>
> Sorry for taking so long to respond...
>
>
> On Thursday 24 November 2016 08:40 PM, Peter Zijlstra wrote:
>> On Thu, Nov 24, 2016 at 08:14:29PM +0530, Hari Bathini wrote:
>>> @@ -862,6 +875,19 @@ enum perf_event_type {
>>>        */
>>>       PERF_RECORD_SWITCH_CPU_WIDE        = 15,
>>>   +    /*
>>> +     * struct {
>>> +     *    struct perf_event_header    header;
>>> +     *
>>> +     *    u32                pid, tid;
>>> +     *    u64                time;
>> pid,tid and time are already present in sample_id. Many of the 'legacy'
>> record have redundant information since we added sample_id, but most of
>> the new ones haven't and rely on sample_all being set.
>
> I tried using pid/tid from sample data, but realized that pid/tid in 
> event_id
> could be different from the one in sample data, at least for 
> fork/namespaces
> events, since __perf_event_header__init_id( ) that updates the sample 
> data
> is getting the pid/tid of current task.
>
> I am not sure if it is advisable to change 
> __perf_event_header__init_id( ) for this..?
>

Hi Peter,

Adding task parameter to __perf_event_header__init_id( ) and doing 
something like..

         perf_event_pid(event, task ? task : current)
         perf_event_tid(event, task ? task : current)


Also, for synthesized events, sample_id is not updated currently. 
Working on it as that
is needed if we want to relay on pid, tid values from sample_id. Let me 
know, if this is
what you had in mind or something else altogether..

Thanks
Hari