From: Stephen Hemminger <stephen@networkplumber.org>
Date: Sun, 25 Jun 2017 19:30:29 +0000 (-0700)
Subject: vmbus: add prefetch to ring buffer iterator
X-Git-Tag: v4.14-rc1~146^2~171
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=15e1674de747d58c5a6154ba6e85bc61e5009b08;p=thirdparty%2Fkernel%2Flinux.git

vmbus: add prefetch to ring buffer iterator

When iterating over incoming ring elements from the host, prefetch
the next descriptor so that it is cache hot.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 741daa6e2fc77..12eb8caa42632 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -357,11 +357,16 @@ static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
 {
 	struct hv_ring_buffer_info *rbi = &channel->inbound;
+	struct vmpacket_descriptor *desc;
 
 	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
 		return NULL;
 
-	return hv_get_ring_buffer(rbi) + rbi->priv_read_index;
+	desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
+	if (desc)
+		prefetch((char *)desc + (desc->len8 << 3));
+
+	return desc;
 }
 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);