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

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Date:   Fri, 17 Feb 2017 00:25:27 +1300
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Hari Bathini <hbathini@...ux.vnet.ibm.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

> +/*
> + * 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.

Eric