[PATCH] hv_vmbus: Add gradually increased delay for retries in vmbus_post_msg()

[PATCH] hv_vmbus: Add gradually increased delay for retries in vmbus_post_msg()

[Haiyang Zhang]

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@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.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

RE: [PATCH] hv_vmbus: Add gradually increased delay for retries in vmbus_post_msg()

[Dexuan Cui]

> -----Original Message-----
> From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On Behalf
> Of Haiyang Zhang
> Sent: Thursday, March 26, 2015 6:59
> To: KY Srinivasan
> Cc: jasowang@redhat.com; Haiyang Zhang; driverdev-
> devel@linuxdriverproject.org; olaf@aepfle.de; linux-kernel@vger.kernel.org
> Subject: [PATCH] hv_vmbus: Add gradually increased delay for retries in
> vmbus_post_msg()
> 
> 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@microsoft.com>
> Reviewed-by: K. Y. Srinivasan <kys@microsoft.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;
>  }

The patch is good to me.

Reviewed-by: Dexuan Cui <decui@microsoft.com>