linux-kernel - [PATCH] virtio/ringtest: fix up need

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Date:   Thu, 26 Oct 2017 04:48:01 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH] virtio/ringtest: fix up need_event math

last kicked event index must be updated unconditionally:
even if we don't need to kick, we do not want to re-check
the same entry for events.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 tools/virtio/ringtest/ring.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/tools/virtio/ringtest/ring.c b/tools/virtio/ringtest/ring.c
index 6b70c4e..d044a88 100644
--- a/tools/virtio/ringtest/ring.c
+++ b/tools/virtio/ringtest/ring.c
@@ -196,16 +196,18 @@ bool enable_call()
 
 void kick_available(void)
 {
+	bool need;
+
 	/* Flush in previous flags write */
 	/* Barrier C (for pairing) */
 	smp_mb();
-	if (!need_event(event->kick_index,
-			guest.avail_idx,
-			guest.kicked_avail_idx))
-		return;
+	need = need_event(event->kick_index,
+			   guest.avail_idx,
+			   guest.kicked_avail_idx);
 
 	guest.kicked_avail_idx = guest.avail_idx;
-	kick();
+	if (need)
+		kick();
 }
 
 /* host side */
@@ -265,14 +267,18 @@ bool use_buf(unsigned *lenp, void **bufp)
 
 void call_used(void)
 {
+	bool need;
+
 	/* Flush in previous flags write */
 	/* Barrier D (for pairing) */
 	smp_mb();
-	if (!need_event(event->call_index,
+
+	need = !need_event(event->call_index,
 			host.used_idx,
-			host.called_used_idx))
-		return;
+			host.called_used_idx);
 
 	host.called_used_idx = host.used_idx;
-	call();
+
+	if (need)
+		call();
 }
-- 
MST