linux-kernel - [PATCH 6/6] vmbus: add prefetch to ring buffer iterator

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Date:   Sun, 25 Jun 2017 12:30:29 -0700
From:   kys@...hange.microsoft.com
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        vkuznets@...hat.com, jasowang@...hat.com,
        leann.ogasawara@...onical.com, marcelo.cerri@...onical.com,
        sthemmin@...rosoft.com
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 6/6] vmbus: add prefetch to ring buffer iterator

From: Stephen Hemminger <stephen@...workplumber.org>

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@...rosoft.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/ring_buffer.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 741daa6..12eb8ca 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);
 
-- 
1.7.1