Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [RFC PATCH 1/1] vhost: TX used buffer guest signal accumulation | From | Shirley Ma <> | Date | Wed, 03 Nov 2010 22:38:46 -0700 |
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On Wed, 2010-11-03 at 12:48 +0200, Michael S. Tsirkin wrote: > I mean in practice, you see a benefit from this patch?
Yes, I tested it. It does benefit the performance.
> > My concern here is whether checking only in set up would be > sufficient > > for security? > > It better be sufficient because the checks that put_user does > are not effictive when run from the kernel thread, anyway. > > > Would be there is a case guest could corrupt the ring > > later? If not, that's OK. > > You mean change the pointer after it's checked? > If you see such a case, please holler.
I wonder about it, not a such case in mind.
> To clarify: the combination of __put_user and separate > signalling is giving the same performance benefit as your > patch?
Yes, it has similar performance, not I haven't finished all message sizes comparison yet.
> I am mostly concerned with adding code that seems to help > speed for reasons we don't completely understand, because > then we might break the optimization easily without noticing.
I don't think the patch I submited would break up anything. It just reduced the cost of per used buffer 3 put_user() calls and guest signaling from one to one to many to one.
Thanks Shirley
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