linux-kernel - Re: [RFC PATCH 00/50] tools/perf: Speed up the build system

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Message-ID: <87y564zvk0.fsf@tassilo.jf.intel.com>
Date:	Mon, 07 Oct 2013 13:15:59 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC PATCH 00/50] tools/perf: Speed up the build system

Ingo Molnar <mingo@...nel.org> writes:
>
> The series also includes a number of fixes and convenience features:
>
>    - auto-detect the number of CPUs on the system and add the -j<cpus>
>      option automatically

FWIW I would prefer if you not do that automatically, because:

- Often the optimal factor is not 1, but something like 1.5*CPUs
(but I'm not sure it's the same on all systems, probably depends on 
the IO capacity and memory)
- It may use a lot of memory, so should be something controlled by the
user.
- Often it's useful to use a few threads less to avoid interactivity
problems on a workstation.
- With LTO there can be rare cases where you need to lower it to avoid
running out of memory.
- Kernel build users should be already trained to set that parameter
and it's not really a big burden.

The rest looks like a great improvement.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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