linux-kernel - Re: [PATCH v6 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

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Message-Id: <45ec7ff8-cddf-56a5-95da-0e46cfb21b60@linux.vnet.ibm.com>
Date:   Mon, 20 Feb 2017 09:46:03 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.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>,
        sargun@...gun.me, Aravinda Prasad <aravinda@...ux.vnet.ibm.com>,
        brendan.d.gregg@...il.com, jolsa@...hat.com
Subject: Re: [PATCH v6 1/3] perf: add PERF_RECORD_NAMESPACES to include
 namespaces related info

Hi Eric,


On Thursday 16 February 2017 04:55 PM, Eric W. Biederman wrote:
>> +/*
>> + * The maximum size of the name of each namespace
>> + */
>> +#define NS_NAME_SIZE				8
>> +
>> +struct perf_ns_link_info {
>> +	char	name[NS_NAME_SIZE];
>> +	__u64	dev;
>> +	__u64	ino;
>> +};
> Ugh. I missed the name the first time around.
>
> That really looks like useless clutter.  You already know the index so
> the name doesn't add any information, so unless I am missing something
> that name will just slow down the perf kernel implementation with
> useless work.
>
> The userspace reader can have the information just as reliably by
> looking at the index and indexing into a table.
>
> The set of namespaces changes slowly enough that this is not likely to
> be a problem in practice.  Especially as perf is released with the
> kernel.
>
> Plus who knows how long the name of the next namespace is going to be.
>

Agreed. Will drop name field from the structure and use an indexing
table to get names in userspace..

Thanks
Hari