linux-kernel - Re: [RFC Patch v1 32/55] ARC: [optim] Cache "current" in Register r25

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Message-Id: <201211121350.12810.arnd@arndb.de>
Date:	Mon, 12 Nov 2012 13:50:12 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Vineet.Gupta1@...opsys.com
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [RFC Patch v1 32/55] ARC: [optim] Cache "current" in Register r25

On Monday 12 November 2012, Vineet.Gupta1@...opsys.com wrote:
> 
>  endmenu # "Platform Board Configuration"
>  
> +config ARC_CURR_IN_REG
> +       bool "Dedicate Register r25 for current_task pointer"
> +       default y
> +       help
> +         This reserved Register R25 to point to Current Task in
> +         kernel mode. This saves memory access for each such access
> +

This looks like a useful feature if you have 32 GPRs, but why make it
optional? Are there cases where you would disable it?

Another alternative to caching "current" would be to cache the per-cpu
offset, and calculate current from that one.

	Arnd
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