netdev - Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

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Message-ID: <CALCETrUY1=jkJTQvCLSSOYw5O9M2N3o1AiT9AnzYE3zQU319TQ@mail.gmail.com>
Date:	Mon, 8 Sep 2014 10:32:07 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	netdev <netdev@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

On Sep 5, 2014 3:55 AM, "Paolo Bonzini" <pbonzini@...hat.com> wrote:
>
> Il 03/09/2014 06:29, Rusty Russell ha scritto:
> > +     desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
> > +     if (!desc)
> > +             return NULL;
> >
> > -     return head;
> > +     for (i = 0; i < total_sg; i++)
> > +             desc[i].next = i+1;
> > +     return desc;
> >  }
>
> Would it make sense to keep a cache of a few (say) 8- or 16-element
> indirect descriptors?  You'd only have to do this ugly (and slowish) for
> loop on the first allocation.
>
> Also, since this is mostly an aesthetic patch,
>
> > +     if (indirect)
> > +             vq->free_head = vq->vring.desc[head].next;
> > +     else
> > +             vq->free_head = i;
>
> I'd move the indirect case above, where the vring.desc[head] is actually
> allocated.
>

Please don't: I'll just have to undo it for the DMA API stuff, since
descriptor setup will be able to fail.

--Andy
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