linux-kernel - Re: [PATCH] MIPS: c-r4k: remove cpu_foreign

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Message-ID: <20150803161845.GG2843@linux-mips.org>
Date:	Mon, 3 Aug 2015 18:18:45 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Paul Burton <paul.burton@...tec.com>
Cc:	linux-mips@...ux-mips.org, Rusty Russell <rusty@...tcorp.com.au>,
	Joshua Kinard <kumba@...too.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Huacai Chen <chenhc@...ote.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Kevin Cernekee <cernekee@...il.com>,
	linux-kernel@...r.kernel.org,
	"Maciej W. Rozycki" <macro@...esourcery.com>,
	Markos Chandras <markos.chandras@...tec.com>,
	Alex Smith <alex.smith@...tec.com>
Subject: Re: [PATCH] MIPS: c-r4k: remove cpu_foreign_map

On Mon, Aug 03, 2015 at 08:54:47AM -0700, Paul Burton wrote:

> Commit cccf34e9411c ("MIPS: c-r4k: Fix cache flushing for MT cores") did
> 2 things:
> 
>   - Introduced cpu_foreign_map to call cache maintenance functions on
>     only a single CPU within each core in the system.
> 
>   - Stopped calling cache maintenance functions on non-local CPUs for
>     systems which include a MIPS Coherence Manager.
> 
> Thus the introduction of cpu_foreign_map has no effect on any systems
> with a CM, since the IPIs will be avoided entirely. Thus it can only
> possibly affect other systems which have multiple logical CPUs per core,
> which appears to only be netlogic. I'm pretty certain this wasn't the
> intent, am unsure whether avoiding such cache maintenance calls is
> correct for netlogic systems and believe the overhead of calculating
> cpu_foreign_map is thus unnecessary & this code is almost certainly
> untested.
> 
> This mostly reverts commit cccf34e9411c ("MIPS: c-r4k: Fix cache
> flushing for MT cores"), leaving only the change for systems with a CM.

BMIPS is another "hyperthreading-like" core.  Maybe Kevin or Florian
can comment if this patch is good for them?

  Ralf
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