linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Message-ID: <4BAA4211.2000209@redhat.com>
Date:	Wed, 24 Mar 2010 18:47:13 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project

On 03/24/2010 06:40 PM, Joerg Roedel wrote:
>
>> Looks trivial to find a guest, less so with enumerating (still doable).
>>      
> Not so trival and even more likely to break. Even it perf has the pid of
> the process and wants to find the directory it has to do:
>
> 1. Get the uid of the process
> 2. Find the username for the uid
> 3. Use the username to find the home-directory
>
> Steps 2. and 3. need nsswitch and/or pam access to get this information
> from whatever source the admin has configured. And depending on what the
> source is it may be temporarily unavailable causing nasty timeouts. In
> short, there are many weak parts in that chain making it more likely to
> break.
>    

It's true.  If the kernel provides something, there are fewer things 
that can break.  But if your system is so broken that you can't resolve 
uids, fix that before running perf.  Must we design perf for that case?

After all, 'ls -l' will break under the same circumstances.  It's hard 
to imagine doing useful work when that doesn't work.

> A kernel-based approach with /proc/<pid>/kvm does not have those issues
> (and to repeat myself, it is independent from the userspace being used).
>    

It has other issues, which are IMO more problematic.

-- 
error compiling committee.c: too many arguments to function

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