2022-03-25 12:10:12

by Xianting Tian

Subject: [PATCH] virtio_ring: remove unnecessary to_vvq call in vring hot path

It passes '_vq' to virtqueue_use_indirect(), which still calls
to_vvq to get 'vq', let's directly pass 'vq'. It can avoid
unnecessary call of to_vvq in hot path.

Other tiny optimization:
Add unlikely to "if (vq->vq.num_free < descs_used).

Signed-off-by: Xianting Tian <[email protected]>
---
drivers/virtio/virtio_ring.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 962f1477b1fa..ab6d5f0cb579 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -205,11 +205,9 @@ struct vring_virtqueue {

#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

-static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
+static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
unsigned int total_sg)
{
- struct vring_virtqueue *vq = to_vvq(_vq);
-
/*
* If the host supports indirect descriptor tables, and we have multiple
* buffers, then go indirect. FIXME: tune this threshold
@@ -507,7 +505,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,

head = vq->free_head;

- if (virtqueue_use_indirect(_vq, total_sg))
+ if (virtqueue_use_indirect(vq, total_sg))
desc = alloc_indirect_split(_vq, total_sg, gfp);
else {
desc = NULL;
@@ -527,7 +525,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
descs_used = total_sg;
}

- if (vq->vq.num_free < descs_used) {
+ if (unlikely(vq->vq.num_free < descs_used)) {
pr_debug("Can't add buf len %i - avail = %i\n",
descs_used, vq->vq.num_free);
/* FIXME: for historical reasons, we force a notify here if
@@ -1194,7 +1192,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,

BUG_ON(total_sg == 0);

- if (virtqueue_use_indirect(_vq, total_sg)) {
+ if (virtqueue_use_indirect(vq, total_sg)) {
err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
in_sgs, data, gfp);
if (err != -ENOMEM) {
--
2.17.1

2022-03-28 12:21:54

by Stefano Garzarella

Subject: Re: [PATCH] virtio_ring: remove unnecessary to_vvq call in vring hot path

On Thu, Mar 24, 2022 at 03:33:40PM +0800, Xianting Tian wrote:
>It passes '_vq' to virtqueue_use_indirect(), which still calls
>to_vvq to get 'vq', let's directly pass 'vq'. It can avoid
>unnecessary call of to_vvq in hot path.

It seems reasonable to me.

>
>Other tiny optimization:
>Add unlikely to "if (vq->vq.num_free < descs_used).

Better to do this change in another patch.

Thanks,
Stefano

>
>Signed-off-by: Xianting Tian <[email protected]>
>---
> drivers/virtio/virtio_ring.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>index 962f1477b1fa..ab6d5f0cb579 100644
>--- a/drivers/virtio/virtio_ring.c
>+++ b/drivers/virtio/virtio_ring.c
>@@ -205,11 +205,9 @@ struct vring_virtqueue {
>
> #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
>
>-static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
>+static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
> unsigned int total_sg)
> {
>- struct vring_virtqueue *vq = to_vvq(_vq);
>-
> /*
> * If the host supports indirect descriptor tables, and we have multiple
> * buffers, then go indirect. FIXME: tune this threshold
>@@ -507,7 +505,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>
> head = vq->free_head;
>
>- if (virtqueue_use_indirect(_vq, total_sg))
>+ if (virtqueue_use_indirect(vq, total_sg))
> desc = alloc_indirect_split(_vq, total_sg, gfp);
> else {
> desc = NULL;
>@@ -527,7 +525,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> descs_used = total_sg;
> }
>
>- if (vq->vq.num_free < descs_used) {
>+ if (unlikely(vq->vq.num_free < descs_used)) {
> pr_debug("Can't add buf len %i - avail = %i\n",
> descs_used, vq->vq.num_free);
> /* FIXME: for historical reasons, we force a notify here if
>@@ -1194,7 +1192,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>
> BUG_ON(total_sg == 0);
>
>- if (virtqueue_use_indirect(_vq, total_sg)) {
>+ if (virtqueue_use_indirect(vq, total_sg)) {
> err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
> in_sgs, data, gfp);
> if (err != -ENOMEM) {
>--
>2.17.1
>

2022-03-28 21:51:45

by Xianting Tian

Subject: Re: [PATCH] virtio_ring: remove unnecessary to_vvq call in vring hot path

在 2022/3/28 下午5:05, Stefano Garzarella 写道:

> On Thu, Mar 24, 2022 at 03:33:40PM +0800, Xianting Tian wrote:
>> It passes '_vq' to virtqueue_use_indirect(), which still calls
>> to_vvq to get 'vq', let's directly pass 'vq'. It can avoid
>> unnecessary call of to_vvq in hot path.
>
> It seems reasonable to me.
>
>>
>> Other tiny optimization:
>> Add unlikely to "if (vq->vq.num_free < descs_used).
>
> Better to do this change in another patch.
Thanks for the reply, I will send the patchset, which contains the two
patches, soon.
>
> Thanks,
> Stefano
>
>>
>> Signed-off-by: Xianting Tian <[email protected]>
>> ---
>> drivers/virtio/virtio_ring.c | 10 ++++------
>> 1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index 962f1477b1fa..ab6d5f0cb579 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -205,11 +205,9 @@ struct vring_virtqueue {
>>
>> #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
>>
>> -static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
>> +static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
>>                       unsigned int total_sg)
>> {
>> -    struct vring_virtqueue *vq = to_vvq(_vq);
>> -
>>     /*
>>      * If the host supports indirect descriptor tables, and we have
>> multiple
>>      * buffers, then go indirect. FIXME: tune this threshold
>> @@ -507,7 +505,7 @@ static inline int virtqueue_add_split(struct
>> virtqueue *_vq,
>>
>>     head = vq->free_head;
>>
>> -    if (virtqueue_use_indirect(_vq, total_sg))
>> +    if (virtqueue_use_indirect(vq, total_sg))
>>         desc = alloc_indirect_split(_vq, total_sg, gfp);
>>     else {
>>         desc = NULL;
>> @@ -527,7 +525,7 @@ static inline int virtqueue_add_split(struct
>> virtqueue *_vq,
>>         descs_used = total_sg;
>>     }
>>
>> -    if (vq->vq.num_free < descs_used) {
>> +    if (unlikely(vq->vq.num_free < descs_used)) {
>>         pr_debug("Can't add buf len %i - avail = %i\n",
>>              descs_used, vq->vq.num_free);
>>         /* FIXME: for historical reasons, we force a notify here if
>> @@ -1194,7 +1192,7 @@ static inline int virtqueue_add_packed(struct
>> virtqueue *_vq,
>>
>>     BUG_ON(total_sg == 0);
>>
>> -    if (virtqueue_use_indirect(_vq, total_sg)) {
>> +    if (virtqueue_use_indirect(vq, total_sg)) {
>>         err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
>>                             in_sgs, data, gfp);
>>         if (err != -ENOMEM) {
>> --
>> 2.17.1
>>