linux-kernel - Re: [PATCH RFC] ARM: extend fixmap mapping region to support 30 CPUs

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Message-ID: <alpine.LFD.2.11.1403241250560.1291@knanqh.ubzr>
Date:	Mon, 24 Mar 2014 16:00:50 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Liu Hua <sdu.liu@...wei.com>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	wangnan0@...wei.com, peifeiyue@...wei.com
Subject: Re: [PATCH RFC] ARM: extend fixmap mapping region to support 30
 CPUs

On Mon, 24 Mar 2014, Liu Hua wrote:

> In 32-bit ARM systems, the fixmap mapping region can support
> no more than 14 CPUs(total: 896k; one CPU: 64K). And we can
> configure NR_CPUS up to 32. So there is a mismatch.
> 
> This patch extends the fixmapping region downwards to boundary
> of DMA mapping region(0xffe00000-0xfffe0000). Then the fixmap
> mapping region can support up to 30 CPUs.

You failed to update CONSISTENT_END in your patch.

Hmmm?  Waitaminute...

Well well...

It looks like the static mapping area for DMA was removed from the code 
by commit e9da6e9905e6 but the information in 
Documentation/arm/memory.txt was not updated accordingly.

CONSISTENT_END in arch/arm/include/asm/memory.h has no more users and 
shoule probably be removed.

This means 0xffc00000 to 0xffefffff is no longer used by anything.

> There seems to be no easy way to support 32 CPUs by simply 
> changing memory layout on ARM Linux. So I also limit the 
> maximal CPU number one can configure.

I think the above should help you solve your CPU limit easily.


Nicolas
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