On 2016/4/26 20:42, Michael S. Tsirkin wrote:
On Tue, Apr 26, 2016 at 04:05:24PM +0800, Zhou Jie wrote:
virtio_net_flush_tx has a huge stack usage of 16392 bytes approx.
Moving large arrays to heap to reduce stack usage.
Signed-off-by: Zhou Jie <zhoujie2...@cn.fujitsu.com>
I don't think it's appropriate for trivial.
Also - what's the point, exactly?
I think functions should not have very large stack frames.
For 64bit machine it will be 32k.
But according what Christian Borntraeger said, it doesn't matter.
So, considerate that virtio_net_flush_tx is in a hot path,
I agree to not change this.
Sincerely,
Zhou Jie
---
hw/net/virtio-net.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 5798f87..cab7bbc 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1213,6 +1213,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
VirtIONet *n = q->n;
VirtIODevice *vdev = VIRTIO_DEVICE(n);
VirtQueueElement *elem;
+ struct iovec *sg = NULL, *sg2 = NULL;
int32_t num_packets = 0;
int queue_index = vq2q(virtio_get_queue_index(q->tx_vq));
if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
@@ -1224,10 +1225,12 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
return num_packets;
}
+ sg = g_new(struct iovec, VIRTQUEUE_MAX_SIZE);
+ sg2 = g_new(struct iovec, VIRTQUEUE_MAX_SIZE + 1);
for (;;) {
ssize_t ret;
unsigned int out_num;
- struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1],
*out_sg;
+ struct iovec *out_sg;
struct virtio_net_hdr_mrg_rxbuf mhdr;
elem = virtqueue_pop(q->tx_vq, sizeof(VirtQueueElement));
@@ -1252,7 +1255,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
virtio_net_hdr_swap(vdev, (void *) &mhdr);
sg2[0].iov_base = &mhdr;
sg2[0].iov_len = n->guest_hdr_len;
- out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1,
+ out_num = iov_copy(&sg2[1], VIRTQUEUE_MAX_SIZE,
out_sg, out_num,
n->guest_hdr_len, -1);
if (out_num == VIRTQUEUE_MAX_SIZE) {
@@ -1269,10 +1272,10 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
*/
assert(n->host_hdr_len <= n->guest_hdr_len);
if (n->host_hdr_len != n->guest_hdr_len) {
- unsigned sg_num = iov_copy(sg, ARRAY_SIZE(sg),
+ unsigned sg_num = iov_copy(sg, VIRTQUEUE_MAX_SIZE,
out_sg, out_num,
0, n->host_hdr_len);
- sg_num += iov_copy(sg + sg_num, ARRAY_SIZE(sg) - sg_num,
+ sg_num += iov_copy(sg + sg_num, VIRTQUEUE_MAX_SIZE - sg_num,
out_sg, out_num,
n->guest_hdr_len, -1);
out_num = sg_num;
@@ -1284,6 +1287,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
if (ret == 0) {
virtio_queue_set_notification(q->tx_vq, 0);
q->async_tx.elem = elem;
+ g_free(sg);
+ g_free(sg2);
return -EBUSY;
}
@@ -1296,6 +1301,8 @@ drop:
break;
}
}
+ g_free(sg);
+ g_free(sg2);
return num_packets;
}
--
2.5.5
.
--
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