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

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Date:   Thu, 16 Feb 2017 12:47:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Hari Bathini <hbathini@...ux.vnet.ibm.com>, 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>,
        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

On Fri, Feb 17, 2017 at 12:25:27AM +1300, 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.

Right; Hari, please ditch that name thing.