From e1f7b4812eab992de46c98b3726745afb042a7f0 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Fri, 30 Nov 2012 00:02:56 +0200 Subject: virtio: limit avail bytes lookahead Commit 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f introduced a regression in virtio-net performance because it looks into the ring aggressively while we really only care about a single packet worth of buffers. Reported as bugzilla 1066055 in launchpad. To fix, add parameters limiting lookahead, and use in virtqueue_avail_bytes. Signed-off-by: Michael S. Tsirkin Reported-by: Edivaldo de Araujo Pereira Tested-by: Edivaldo de Araujo Pereira Reviewed-by: Stefan Hajnoczi Signed-off-by: Anthony Liguori --- hw/virtio-rng.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) (limited to 'hw/virtio-rng.c') diff --git a/hw/virtio-rng.c b/hw/virtio-rng.c index df329f2..a73ef8e 100644 --- a/hw/virtio-rng.c +++ b/hw/virtio-rng.c @@ -43,11 +43,11 @@ static bool is_guest_ready(VirtIORNG *vrng) return false; } -static size_t get_request_size(VirtQueue *vq) +static size_t get_request_size(VirtQueue *vq, unsigned quota) { unsigned int in, out; - virtqueue_get_avail_bytes(vq, &in, &out); + virtqueue_get_avail_bytes(vq, &in, &out, quota, 0); return in; } @@ -84,12 +84,18 @@ static void chr_read(void *opaque, const void *buf, size_t size) static void virtio_rng_process(VirtIORNG *vrng) { size_t size; + unsigned quota; if (!is_guest_ready(vrng)) { return; } - size = get_request_size(vrng->vq); + if (vrng->quota_remaining < 0) { + quota = 0; + } else { + quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX); + } + size = get_request_size(vrng->vq, quota); size = MIN(vrng->quota_remaining, size); if (size) { rng_backend_request_entropy(vrng->rng, size, chr_read, vrng); -- cgit v1.1