netdev - Re: [PATCH 2/3] x86_64: Define 128-bit memory-mapped I/O operations

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Message-ID: <1345601051.2659.93.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Wed, 22 Aug 2012 03:04:11 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, <netdev@...r.kernel.org>,
	<linux-net-drivers@...arflare.com>, <x86@...nel.org>
Subject: Re: [PATCH 2/3] x86_64: Define 128-bit memory-mapped I/O operations

On Tue, 2012-08-21 at 18:37 -0700, H. Peter Anvin wrote:
> On 08/21/2012 06:23 PM, Ben Hutchings wrote:
> > Define reado(), writeo() and their raw counterparts using SSE.
> > 
> > Based on work by Stuart Hodgson <smhodgson@...arflare.com>.
> 
> It would be vastly better if we explicitly controlled this with
> kernel_fpu_begin()/kernel_fpu_end() rather than hiding it in primitives
> than might tempt the user to do very much the wrong thing.
> 
> Also, it needs to be extremely clear to the user that these operations
> use the FPU, and all the requirements there need to be met, including
> not using them at interrupt time.

Well we can sometimes use the FPU state at IRQ time, can't we
(irq_fpu_usable())?   So we might need, say, try_reado() and
try_writeo() with callers expected to fall back to alternatives.  (Which
they must have anyway for any architecture that doesn't support this.)

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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