Re: [Xen-devel] [PATCH] Enble 6 argument hypercalls for HVMs

To:	Jan Beulich <JBeulich@xxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] Enble 6 argument hypercalls for HVMs
From:	Keir Fraser <keir@xxxxxxx>
Date:	Wed, 15 Dec 2010 13:20:46 +0000
Cc:	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date:	Wed, 15 Dec 2010 05:21:47 -0800
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On 15/12/2010 12:12, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> On 15.12.10 at 12:43, Keir Fraser <keir@xxxxxxx> wrote:
>> On 15/12/2010 10:40, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>> Looking at this code also makes me wonder once again whether
>>> it really is a good idea to have a generally not taken forward
>>> branch here.
>> 
>> Which generally not-taken branch? The 'je 1f' instruction generally *will*
>> be taken!
> 
> Oops, of course - it being taken is the problem, as it'll be statically
> mis-predicted.

Well, moving the trace code out of line, perhaps into the fixup section,
would be good for cache locality. And then we would have a rarely taken
forward branch (since the fixup section comes after normal text).

I'm sure there are a bunch of places in our asm code where we could do this.
Feel free to fix them all up, if you like.

 -- Keir

> Jan
> 

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Re: [Xen-devel] [PATCH] Enble 6 argument hypercalls for HVMs