linux-kernel - Re: [PATCH] arm: Preserve TPIDRURW on context switch

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Date:	Wed, 6 Feb 2013 22:51:50 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	André Hentschel <nerv@...ncrow.de>
Cc:	linux-arch@...r.kernel.org, will.deacon@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] arm: Preserve TPIDRURW on context switch

On Wed, Feb 06, 2013 at 11:43:10PM +0100, André Hentschel wrote:
> There are more and more applications coming to WinRT, Wine could support them,
> but mostly they expect to have the thread environment block (TEB) in TPIDRURW.
> This register must be preserved per thread instead of being cleared.

I'd prefer this was done a little more sensitively to those CPUs where
loads/stores are expensive, namely:

> +
> +	@ preserve TPIDRURW register state
> +	get_tls2	r3, r4, r5
> +	str	r3, [r1, #TI_TP2_VALUE]
> +	ldr	r3, [r2, #TI_TP2_VALUE]
> +	set_tls2	r3, r4, r5

those two loads/stores get omitted from the thread switching if the CPU
doesn't support it.  Do you think that's something you could do?
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