From 54451599195d242c8ea93b45adc43a161c44111c Mon Sep 17 00:00:00 2001 From: Amos Kong Date: Tue, 10 Sep 2013 06:08:02 +0200 Subject: [PATCH 20/39] virtio: limit avail bytes lookahead RH-Author: Amos Kong Message-id: <1378793288-3371-21-git-send-email-akong@redhat.com> Patchwork-id: 54255 O-Subject: [RHEL-6.5 qemu-kvm PATCH v3 20/26] virtio: limit avail bytes lookahead Bugzilla: 786407 RH-Acked-by: Paolo Bonzini RH-Acked-by: Amit Shah RH-Acked-by: Laszlo Ersek From: Michael S. Tsirkin 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 (cherry picked from commit e1f7b4812eab992de46c98b3726745afb042a7f0) Droped the small change in hw/virtio-serial-bus.c, no effect Signed-off-by: Amos Kong --- hw/virtio-rng.c | 12 +++++++++--- hw/virtio.c | 15 ++++++++------- hw/virtio.h | 3 ++- 3 files changed, 19 insertions(+), 11 deletions(-) Signed-off-by: Miroslav Rezanina --- hw/virtio-rng.c | 12 +++++++++--- hw/virtio.c | 15 ++++++++------- hw/virtio.h | 3 ++- 3 files changed, 19 insertions(+), 11 deletions(-) diff --git a/hw/virtio-rng.c b/hw/virtio-rng.c index 595352d..b7e3e12 100644 --- a/hw/virtio-rng.c +++ b/hw/virtio-rng.c @@ -44,11 +44,11 @@ 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; } @@ -85,12 +85,18 @@ 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); diff --git a/hw/virtio.c b/hw/virtio.c index 0bd3912..e5eeabd 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -340,7 +340,8 @@ static unsigned virtqueue_next_desc(target_phys_addr_t desc_pa, } void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, - unsigned int *out_bytes) + unsigned int *out_bytes, + unsigned max_in_bytes, unsigned max_out_bytes) { unsigned int idx; unsigned int total_bufs, in_total, out_total; @@ -389,6 +390,9 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, } else { out_total += vring_desc_len(desc_pa, i); } + if (in_total >= max_in_bytes && out_total >= max_out_bytes) { + goto done; + } } while ((i = virtqueue_next_desc(desc_pa, i, max)) != max); if (!indirect) @@ -396,6 +400,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, else total_bufs++; } +done: if (in_bytes) { *in_bytes = in_total; } @@ -409,12 +414,8 @@ int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, { unsigned int in_total, out_total; - virtqueue_get_avail_bytes(vq, &in_total, &out_total); - if ((in_bytes && in_bytes < in_total) - || (out_bytes && out_bytes < out_total)) { - return 1; - } - return 0; + virtqueue_get_avail_bytes(vq, &in_total, &out_total, in_bytes, out_bytes); + return in_bytes <= in_total && out_bytes <= out_total; } void virtqueue_map_sg(struct iovec *sg, target_phys_addr_t *addr, diff --git a/hw/virtio.h b/hw/virtio.h index fbf3aea..1773654 100644 --- a/hw/virtio.h +++ b/hw/virtio.h @@ -156,7 +156,8 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem); int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, unsigned int out_bytes); void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, - unsigned int *out_bytes); + unsigned int *out_bytes, + unsigned max_in_bytes, unsigned max_out_bytes); void virtio_notify(VirtIODevice *vdev, VirtQueue *vq); -- 1.7.1