On 2019/10/11 下午9:45, Michael S. Tsirkin wrote:
The idea is to support multiple ring formats by converting
to a format-independent array of descriptors.
This costs extra cycles, but we gain in ability
to fetch a batch of descriptors in one go, which
is good for code cache locality.
To simplify benchmarking, I kept the old code
around so one can switch back and forth by
writing into a module parameter.
This will go away in the final submission.
This patch causes a minor performance degradation,
it's been kept as simple as possible for ease of review.
Next patch gets us back the performance by adding batching.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
drivers/vhost/test.c | 17 ++-
drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++-
drivers/vhost/vhost.h | 16 +++
3 files changed, 327 insertions(+), 5 deletions(-)
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 056308008288..39a018a7af2d 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -18,6 +18,9 @@
#include "test.h"
#include "vhost.h"
+static int newcode = 0;
+module_param(newcode, int, 0644);
+
/* Max number of bytes transferred before requeueing the job.
* Using this limit prevents one virtqueue from starving others. */
#define VHOST_TEST_WEIGHT 0x80000
@@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n)
vhost_disable_notify(&n->dev, vq);
for (;;) {
- head = vhost_get_vq_desc(vq, vq->iov,
- ARRAY_SIZE(vq->iov),
- &out, &in,
- NULL, NULL);
+ if (newcode)
+ head = vhost_get_vq_desc_batch(vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in,
+ NULL, NULL);
+ else
+ head = vhost_get_vq_desc(vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in,
+ NULL, NULL);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 36ca2cf419bf..36661d6cb51f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
{
vq->num = 1;
+ vq->ndescs = 0;
vq->desc = NULL;
vq->avail = NULL;
vq->used = NULL;
@@ -369,6 +370,9 @@ static int vhost_worker(void *data)
static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
{
+ kfree(vq->descs);
+ vq->descs = NULL;
+ vq->max_descs = 0;
kfree(vq->indirect);
vq->indirect = NULL;
kfree(vq->log);
@@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
for (i = 0; i < dev->nvqs; ++i) {
vq = dev->vqs[i];
+ vq->max_descs = dev->iov_limit;
+ vq->descs = kmalloc_array(vq->max_descs,
+ sizeof(*vq->descs),
+ GFP_KERNEL);
Is iov_limit too much here? It can obviously increase the footprint. I
guess the batching can only be done for descriptor without indirect or
next set. Then we may batch 16 or 64.
Thanks
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