linux-kernel - Re: [PATCH v2 2/2] virtio-ring: Allocate indirect buffers from cache when possible

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Message-ID: <20120907000623.GA3000@redhat.com>
Date:	Fri, 7 Sep 2012 03:06:23 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] virtio-ring: Allocate indirect buffers from cache
 when possible

On Fri, Sep 07, 2012 at 09:19:04AM +0930, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@...hat.com> writes:
> 
> > On Thu, Sep 06, 2012 at 05:27:23PM +0930, Rusty Russell wrote:
> >> "Michael S. Tsirkin" <mst@...hat.com> writes:
> >> > Yes without checksum net core always linearizes packets, so yes it is
> >> > screwed.
> >> > For -net, skb always allocates space for 17 frags + linear part so
> >> > it seems sane to do same in virtio core, and allocate, for -net,
> >> > up to max_frags + 1 from cache.
> >> > We can adjust it: no _SG -> 2 otherwise 18.
> >> 
> >> But I thought it used individual buffers these days?
> >
> > Yes for receive, no for transmit. That's probably why
> > we should have the threshold per vq, not per device, BTW.
> 
> Can someone actually run with my histogram patch and see what the real
> numbers are?
> 
> I'm not convinced that the ideal 17-buffer case actually happens as much
> as we think.  And if it's not happening with this netperf test, we're
> testing the wrong thing.
> 
> Thanks,
> Rusty.

hope to play with it next week
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