linux-kernel - Re: [PATCHv2] arm: Preserve TPIDRURW on context switch

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Message-ID: <20130422151836.GA15665@mudshark.cambridge.arm.com>
Date:	Mon, 22 Apr 2013 16:18:37 +0100
From:	Will Deacon <will.deacon@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	André Hentschel <nerv@...ncrow.de>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: [PATCHv2] arm: Preserve TPIDRURW on context switch

On Mon, Apr 22, 2013 at 03:36:16PM +0100, Russell King - ARM Linux wrote:
> On Fri, Apr 19, 2013 at 05:54:35PM +0200, André Hentschel wrote:
> > From: =?UTF-8?q?Andr=C3=A9=20Hentschel?= <nerv@...ncrow.de>
> > 
> > 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.
> > 
> > Signed-off-by: André Hentschel <nerv@...ncrow.de>
> 
> This actually makes things less efficient all round, because you
> now use the value immediately after loading, which means it will cause
> pipeline stalls, certainly on older CPUs.
> 
> Could you please rework the patch to try avoiding soo many modifications
> to the way things have been done here?

copy_thread also needs updating so that the *register* value for the parent
is copied to the child, since the parent may have written the register
after the last context-switch, meaning that tp_value is out-of-date.

Will
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