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[Qemu-devel] [PATCH] virtio: limit avail bytes lookahead
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] [PATCH] virtio: limit avail bytes lookahead |
Date: |
Thu, 1 Nov 2012 18:07:21 +0200 |
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.
To fix, add parameters limiting lookahead, and
use in virtqueue_avail_bytes.
Signed-off-by: Michael S. Tsirkin <address@hidden>
Reported-by: Edivaldo de Araujo Pereira <address@hidden>
---
Edivaldo could you please confirm this fixes regression?
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index d20bd8b..a761cdc 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -297,7 +297,7 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port)
if (use_multiport(port->vser) && !port->guest_connected) {
return 0;
}
- virtqueue_get_avail_bytes(vq, &bytes, NULL);
+ virtqueue_get_avail_bytes(vq, &bytes, NULL, UINT_MAX, 0);
return bytes;
}
diff --git a/hw/virtio.c b/hw/virtio.c
index ec8b7d8..f40a8c5 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -336,7 +336,8 @@ static unsigned virtqueue_next_desc(hwaddr 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;
@@ -385,6 +386,9 @@ 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)
@@ -392,6 +396,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int
*in_bytes,
else
total_bufs++;
}
+done:
if (in_bytes) {
*in_bytes = in_total;
}
@@ -405,12 +410,8 @@ 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, hwaddr *addr,
diff --git a/hw/virtio.h b/hw/virtio.h
index ac482be..1278328 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -150,7 +150,8 @@ 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);
- Re: [Qemu-devel] [Bug 1066055] Re: Network performance regression with vde_switch, Amit Shah, 2012/11/01
- Re: [Qemu-devel] [Bug 1066055] Re: Network performance regression with vde_switch, Michael S. Tsirkin, 2012/11/01
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Michael S. Tsirkin, 2012/11/27
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Edivaldo de Araujo Pereira, 2012/11/27
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Anthony Liguori, 2012/11/27
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Michael S. Tsirkin, 2012/11/28
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Amit Shah, 2012/11/29
- Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead, Michael S. Tsirkin, 2012/11/29