linux-kernel - Re: [PATCH v4 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

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Date:   Fri, 16 Dec 2016 08:57:03 +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 v4 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info

On Fri, Dec 16, 2016 at 11:57:47AM +0530, Hari Bathini wrote:
> 
> 
> On Friday 16 December 2016 12:16 AM, Peter Zijlstra wrote:
> >On Fri, Dec 16, 2016 at 12:07:06AM +0530, Hari Bathini wrote:
> >>+struct perf_ns_link_info {
> >>+	__u64	dev;
> >>+	__u64	ino;
> >>+};
> >>+
> >>+enum {
> >>+	NET_NS_INDEX		= 0,
> >>+	UTS_NS_INDEX		= 1,
> >>+	IPC_NS_INDEX		= 2,
> >>+	PID_NS_INDEX		= 3,
> >>+	USER_NS_INDEX		= 4,
> >>+	MNT_NS_INDEX		= 5,
> >>+	CGROUP_NS_INDEX		= 6,
> >>+
> >>+	NAMESPACES_MAX,		/* maximum available namespaces */
> >>+};
> >>+
> >>  enum perf_event_type {
> >>  	/*
> >>@@ -862,6 +880,17 @@ enum perf_event_type {
> >>  	 */
> >>  	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
> >>+	/*
> >>+	 * struct {
> >>+	 *	struct perf_event_header	header;
> >>+	 *	u32				pid;
> >>+	 *	u32				tid;
> >>+	 *	struct namespace_link_info	link_info[NAMESPACES_MAX];
> >>+	 *	struct sample_id		sample_id;
> >>+	 * };
> >>+	 */
> >>+	PERF_RECORD_NAMESPACES			= 16,
> >>+
> >>  	PERF_RECORD_MAX,			/* non-ABI */
> >>  };
> >What happens if a future kernel adds another namespace?
> >
> 
> No impact unless NAMESPACES_MAX in include/uapi/linux/perf_event.h is
> updated to accommodate that..
> And if it is updated, the corresponding change is expected in perf-tool as
> well..

And what happens if you try and process old data files with the new
tools or the other way around?

You must not expect lock-step updates for this to work.