Re: [PATCH] virtio_net: Check for room in the vq before adding buffer

[Amit Shah <amit.shah@redhat.com>]

On (Thu) Aug 27 2009 [19:17:20], Rusty Russell wrote:
> On Wed, 26 Aug 2009 06:58:28 pm Amit Shah wrote:
> > Saves us one cycle of alloc-add-free if the queue was full.
> > 
> > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> 
> Thanks, applied with one change:
> 
> > @@ -323,7 +323,7 @@ static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
> >  			break;
> >  		}
> >  		vi->num++;
> > -	}
> > +	} while (err > 0);
> 
> This is better as "while (err >= num)".  The other one is right (we only need
> 1 buffer), this one we need to be able to fit "num" entries.

I'm missing something though: the value of 'num' changes in the loop and
the value of num when it will be compared will just have been used by
add_buf. The next iteration of the loop will probably use a different
value (-- from just reading the code, not going over the cases in which
this function is called).

		Amit