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Date: Wed, 24 Nov 2010 19:36:34 -0500
Message-ID: <AANLkTikwo+tdyiT=L9TOyN3Pk8nqpibdokN1X5mZx-pZ@mail.gmail.com>
Subject: Re: [RFC 2/2] x86, xsave: rework xsave support
From: Brian Gerst <brgerst@gmail.com>
To: Hans Rosenfeld <hans.rosenfeld@amd.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, robert.richter@amd.com,
        andreas.herrmann3@amd.com
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On Tue, Nov 23, 2010 at 3:41 PM, Hans Rosenfeld <hans.rosenfeld@amd.com> wrote:
> This is an attempt to rework the code that handles FPU and related
> extended states. Since FPU, XMM and YMM states are just variants of what
> xsave handles, all of the old FPU-specific state handling code will be
> hidden behind a set of functions that resemble xsave and xrstor. For
> hardware that does not support xsave, the code falls back to
> fxsave/fxrstor or even fsave/frstor.
>
> A xstate_mask member will be added to the thread_info structure that
> will control which states are to be saved by xsave. It is set to include
> all "lazy" states (that is, all states currently supported) by the #NM
> handler when a lazy restore is triggered or by switch_to() when the
> tasks FPU context is preloaded. Xstate_mask is intended to completely
> replace TS_USEDFPU in a later cleanup patch.
>
> When "non-lazy" states such as for LWP will be added later, the
> corresponding bits in xstate_mask are supposed to be set for all threads
> all the time. There will be no performance penalty for threads not using
> these states, as xsave and xrstor will ignore unused states.
>
> This patch is not complete and not final at all. Support for 32bit is
> lacking, and the context handling for signals will probably change
> again. I haven't benchmarked it yet, but I have tested it for both the
> fxsave and xsave cases.

Looks good, but I would suggest adding wrappers for save_states() and
restore_xstates() that handle preemption, like how unlazy_fpu() was.

--
Brian Gerst
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