Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH RFC 2/3] virtio_net: fix tx capacity checks using new API | Date | Thu, 02 Jun 2011 11:40:26 +0930 |
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On Wed, 1 Jun 2011 12:49:54 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote: > In the (rare) case where new descriptors are used > while virtio_net enables vq callback for the TX vq, > virtio_net uses the number of sg entries in the skb it frees to > calculate how many descriptors in the ring have just been made > available. But this value is an overestimate: with indirect buffers > each skb only uses one descriptor entry, meaning we may wake the queue > only to find we still can't transmit anything.
This is a bit misleading.
The value is an overestimate, but so is the requirement for 2+MAX_SKB_FRAGS, *unless* we suddenly drop into direct mode due to OOM.
Thanks, Rusty.
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