linux-kernel - [PATCH 7/7] hv_vmbus: Add gradually increased delay for retries in vmbus_post

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Message-Id: <1427472614-32625-7-git-send-email-kys@microsoft.com>
Date:	Fri, 27 Mar 2015 09:10:14 -0700
From:	"K. Y. Srinivasan" <kys@...rosoft.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
Cc:	Haiyang Zhang <haiyangz@...rosoft.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 7/7] hv_vmbus: Add gradually increased delay for retries in vmbus_post_msg()

From: Haiyang Zhang <haiyangz@...rosoft.com>

Most of the retries can be done within a millisecond successfully, so we
sleep 1ms before the first retry, then gradually increase the retry
interval to 2^n with max value of 2048ms. Doing so, we will have shorter
overall delay time, because most of the cases succeed within 1-2 attempts.

Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
Reviewed-by: K. Y. Srinivasan <kys@...rosoft.com>
Reviewed-by: Dexuan Cui <decui@...rosoft.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/connection.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 583d7d4..b27220a 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -422,6 +422,7 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 	union hv_connection_id conn_id;
 	int ret = 0;
 	int retries = 0;
+	u32 msec = 1;
 
 	conn_id.asu32 = 0;
 	conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;
@@ -431,7 +432,7 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 	 * insufficient resources. Retry the operation a couple of
 	 * times before giving up.
 	 */
-	while (retries < 10) {
+	while (retries < 20) {
 		ret = hv_post_message(conn_id, 1, buffer, buflen);
 
 		switch (ret) {
@@ -454,7 +455,9 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 		}
 
 		retries++;
-		msleep(1000);
+		msleep(msec);
+		if (msec < 2048)
+			msec *= 2;
 	}
 	return ret;
 }
-- 
1.7.4.1

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