RE: [Xen-devel] Add multi-page shared ring support toxen-blkfront/back

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> On Tue, 2010-01-12 at 15:58 -0500, James Harper wrote:
> 
> > I received the 1/2 and 2/2 emails containing the patches.
> >
> > Is there any measurable performance increase with this update? I assume
> > it means that you can have more read/write operations on the ring at
> > once? What would be useful to me is larger read/write operations...
> 
> Interesting. Why? Asking because ring space is spent on segments, not
> request headers. Do you see a notable difference somewhere, compared to
> a bunch of (virtually) consecutive request ranges? Or rather a
> convenience thing for the gpl PV drivers?
> 

Windows has a limit to the number of outstanding requests that it will issue. 
It is as low as 16 under some versions of their scsiport infrastructure. I 
think storport relaxes those limits a bit but I haven't gotten as far as a 
storport driver yet.

So larger requests would probably benefit windows more than more requests would.

It would be nice if the ring slots could be dynamic in size. Major rewrite of 
everything of course, but we'd get the best of both worlds.

James

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