linux-kernel - [PATCH 2/3] vdpa_sim_blk: limit the number of request handled per batch

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Date:   Tue, 21 Jun 2022 18:08:58 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     virtualization@...ts.linux-foundation.org
Cc:     Jason Wang <jasowang@...hat.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org,
        Stefano Garzarella <sgarzare@...hat.com>
Subject: [PATCH 2/3] vdpa_sim_blk: limit the number of request handled per batch

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@...hat.com>
Signed-off-by: Stefano Garzarella <sgarzare@...hat.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);
+
 			/* Make sure used is visible before rasing the interrupt. */
 			smp_wmb();
 
@@ -218,10 +223,18 @@ static void vdpasim_blk_work(struct work_struct *work)
 			if (vringh_need_notify_iotlb(&vq->vring) > 0)
 				vringh_notify(&vq->vring);
 			local_bh_enable();
+
+			if (++reqs > 4) {
+				vq_work = false;
+				reschedule = true;
+			}
 		}
 	}
 out:
 	spin_unlock(&vdpasim->lock);
+
+	if (reschedule)
+		schedule_work(&vdpasim->work);
 }
 
 static void vdpasim_blk_get_config(struct vdpasim *vdpasim, void *config)
-- 
2.36.1