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

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Date:   Wed, 21 Dec 2016 18:39:01 +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 v4 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info

Hi Peter,


On Saturday 17 December 2016 01:35 AM, Peter Zijlstra wrote:
> On Fri, Dec 16, 2016 at 11:51:20PM +0530, Hari Bathini wrote:
>> Hi Peter,
>>
>>
>> On Friday 16 December 2016 01:27 PM, Peter Zijlstra wrote:
>>> 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?
>> It works fine either way. I tested that..
> I don't see how the tool can parse old records (with NAMESPACES_MAX ==
> 7) if you set its NAMESPACES_MAX to say 10.
>
> Then it will expect the link_info array to be 10 entries and either read
> past the end of the record (if !sample_all) or try and interpret
> sample_id as link_info records.
>

Right. There will be inconsistency with data the perf tool tries to read 
beyond
what the kernel supports. IIUC, you mean, include nr_namespaces field in the
record and warn the user if it doesn't match with the one perf-tool supports
before proceeding..?

Thanks
Hari

PS: I am on vacation. Will post next version early January.