Re: [PATCH 0/2] Batch writes to MMIO

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le mercredi 23 avril 2008 à 17:05 +0300, Avi Kivity a écrit :
> Laurent Vivier wrote:
> > These two patches allow to batch writes to MMIO.
> >
> > When kernel has to send MMIO writes to userspace, it stores them
> > in memory until it has to pass the hand to userspace for another
> > reason. This avoids to have too many context switches on operations
> > that can wait.
> >
> >   
> 
> Did you obtain any measurable performance benefit?

Well, the problem is how to measure it. Really, I don't know.

But when I add traces I saw MMIO writes are batched: by group of 170
(this is the max in a page) at the beginning, and by group of 10 with XP
when we move a window.

So all comments are welcome...

> > WARNING: this breaks compatibility with old userspace part.
> >
> >   
> 
> So it's just an RFC :)

Yes... to have some comments how to manage this :)

Laurent
-- 
------------- Laurent.Vivier@bull.net ---------------
"The best way to predict the future is to invent it."
- Alan Kay


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