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

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Message-ID: <20161209140913.GO3107@twins.programming.kicks-ass.net>
Date:   Fri, 9 Dec 2016 15:09:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hari Bathini <hbathini@...ux.vnet.ibm.com>
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 Fri, Dec 09, 2016 at 12:10:20AM +0530, 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.

Ah indeed. Yes please disregard my comment then.