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:

quoted

Define reado(), writeo() and their raw counterparts using SSE.

Based on work by Stuart Hodgson [off-list ref].

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
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