Re: [Xen-devel] [Hackathon minutes] PV block improvements

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jun 24, 2013 at 11:09:19PM -0700, Matt Wilson wrote:
> On Sat, Jun 22, 2013 at 09:11:20AM +0200, Roger Pau Monné wrote:
> > On 21/06/13 20:07, Matt Wilson wrote:
> > > On Fri, Jun 21, 2013 at 07:10:59PM +0200, Roger Pau Monné wrote:
> 
> [...]
> 
> > >> 2. Switch to grant copy in blkback, and get rid of persistent grants (I
> > >> have not benchmarked this solution, but I'm quite sure it will involve a
> > >> performance regression, specially when scaling to a high number of 
> > >> domains).
> > > 
> > > Why do you think so?
> > 
> > First because grant_copy is done by the hypervisor, while when using
> > persistent grants the copy is done by the guest. Also, grant_copy takes
> > the grant lock, so when scaling to a large number of domains there's
> > going to be contention around this lock. Persistent grants don't need
> > any shared lock, and thus scale better.
> 
> It'd benefit xen-netback to make the locking in the copy path more
> fine grained. That would help multi-vif domUs today, and multi-queue
> vifs later on.
> 

I'm not sure I follow. I presume you mean using persistent grant in
xen-netback to help scale better?


Wei.

> Thoughts?
> 
> --msw
> 
> 
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