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SubjectRe: [PATCH 2/3] vdpa_sim_blk: limit the number of request handled per batch
On Thu, Jun 23, 2022 at 11:50:22AM +0800, Jason Wang wrote:
>On Wed, Jun 22, 2022 at 12:09 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>>
>> Limit the number of requests (4 per queue as for vdpa_sim_net) handled
>> in a batch to prevent the worker from using the CPU for too long.
>>
>> Suggested-by: Eugenio Pérez <eperezma@redhat.com>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c | 15 ++++++++++++++-
>> 1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>> index a83a5c76f620..ac86478845b6 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>> @@ -197,6 +197,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
>> static void vdpasim_blk_work(struct work_struct *work)
>> {
>> struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
>> + bool reschedule = false;
>> int i;
>>
>> spin_lock(&vdpasim->lock);
>> @@ -206,11 +207,15 @@ static void vdpasim_blk_work(struct work_struct *work)
>>
>> for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
>> struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
>> + bool vq_work = true;
>> + int reqs = 0;
>>
>> if (!vq->ready)
>> continue;
>>
>> - while (vdpasim_blk_handle_req(vdpasim, vq)) {
>> + while (vq_work) {
>> + vq_work = vdpasim_blk_handle_req(vdpasim, vq);
>> +
>
>Is it better to check and exit the loop early here?

Maybe, but I'm not sure.

In vdpa_sim_net we call vringh_complete_iotlb() and send notification
also in the error path, so I thought was better to send notification
also when vdpasim_blk_handle_req() return false, since we will update
the used.idx.

However, I don't think it's a common path, so if you think it's better
to exit the loop early, I can do it.

Thanks,
Stefano

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