Re: [PATCHv2 RFC 4/4] Revert "virtio: make add_buf return capacity remaining:
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2011-06-07 15:54:57
On Thu, Jun 02, 2011 at 06:43:25PM +0300, Michael S. Tsirkin wrote:
This reverts commit 3c1b27d5043086a485f8526353ae9fe37bfa1065. The only user was virtio_net, and it switched to min_capacity instead. Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
It turns out another place in virtio_net: receive
buf processing - relies on the old behaviour:
try_fill_recv:
do {
if (vi->mergeable_rx_bufs)
err = add_recvbuf_mergeable(vi, gfp);
else if (vi->big_packets)
err = add_recvbuf_big(vi, gfp);
else
err = add_recvbuf_small(vi, gfp);
oom = err == -ENOMEM;
if (err < 0)
break;
++vi->num;
} while (err > 0);
The point is to avoid allocating a buf if
the ring is out of space and we are sure
add_buf will fail.
It works well for mergeable buffers and for big
packets if we are not OOM. small packets and
oom will do extra get_page/put_page calls
(but maybe we don't care).
So this is RX, I intend to drop it from this patchset and focus on the
TX side for starters.
quoted hunk
--- drivers/virtio/virtio_ring.c | 2 +- include/linux/virtio.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 23422f1..a6c21eb 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c@@ -233,7 +233,7 @@ add_head: pr_debug("Added buffer head %i to %p\n", head, vq); END_USE(vq); - return vq->num_free; + return 0; } EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);diff --git a/include/linux/virtio.h b/include/linux/virtio.h index 209220d..63c4908 100644 --- a/include/linux/virtio.h +++ b/include/linux/virtio.h@@ -34,7 +34,7 @@ struct virtqueue { * in_num: the number of sg which are writable (after readable ones) * data: the token identifying the buffer. * gfp: how to do memory allocations (if necessary). - * Returns remaining capacity of queue (sg segments) or a negative error. + * Returns 0 on success or a negative error. * virtqueue_kick: update after add_buf * vq: the struct virtqueue * After one or more add_buf calls, invoke this to kick the other side.-- 1.7.5.53.gc233e