Linux Virtualization - May 2010 - [PATCH 1/1] staging: hv: Optimize adj_guesttime function and add more detailed comments

From: Haiyang Zhang <haiyangz at microsoft.com>

Subject: Optimize adj_guesttime function and add more detailed comments
Credits go to Joe Perches [joe at perches.com] for suggesting the changes.

Cc: Greg Kroah-Hartman <gregkh at suse.de>
Signed-off-by: Hank Janssen <hjanssen at microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz at microsoft.com>

---
 drivers/staging/hv/hv_utils.c |   33 +++++++++++++++++++++++++--------
 1 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/hv/hv_utils.c b/drivers/staging/hv/hv_utils.c
index 8f1d3ba..c0f57a1 100644
--- a/drivers/staging/hv/hv_utils.c
+++ b/drivers/staging/hv/hv_utils.c
@@ -106,28 +106,45 @@ static void shutdown_onchannelcallback(void *context)
 		orderly_poweroff(false);
 }
 
-
 /*
- * Synchronize time with host after reboot, restore, etc.
+ * Set guest time to host UTC time.
  */
-static void adj_guesttime(u64 hosttime, u8 flags)
+static inline void do_adj_guesttime(u64 hosttime)
 {
 	s64 host_tns;
 	struct timespec host_ts;
-	static s32 scnt = 50;
 
 	host_tns = (hosttime - WLTIMEDELTA) * 100;
 	host_ts = ns_to_timespec(host_tns);
 
+	do_settimeofday(&host_ts);
+
+	return;
+}
+
+/*
+ * Synchronize time with host after reboot, restore, etc.
+ *
+ * ICTIMESYNCFLAG_SYNC flag bit indicates reboot, restore events of the VM.
+ * After reboot the flag ICTIMESYNCFLAG_SYNC is included in the first time
+ * message after the timesync channel is opened. Since the hv_utils module is
+ * loaded after hv_vmbus, the first message is usually missed. The other
+ * thing is, systime is automatically set to emulated hardware clock which may
+ * not be UTC time or in the same time zone. So, to override these effects, we
+ * use the first 50 time samples for initial system time setting.
+ */
+static inline void adj_guesttime(u64 hosttime, u8 flags)
+{
+	static s32 scnt = 50;
+
 	if ((flags & ICTIMESYNCFLAG_SYNC) != 0) {
-		do_settimeofday(&host_ts);
+		do_adj_guesttime(hosttime);
 		return;
 	}
 
-	if ((flags & ICTIMESYNCFLAG_SAMPLE) != 0 &&
-	    scnt > 0) {
+	if ((flags & ICTIMESYNCFLAG_SAMPLE) != 0 && scnt > 0) {
 		scnt--;
-		do_settimeofday(&host_ts);
+		do_adj_guesttime(hosttime);
 	}
 
 	return;
-- 
1.6.3.2

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On Mon, 2010-05-10 at 18:12 +0000, Haiyang Zhang wrote:
> diff --git a/drivers/staging/hv/hv_utils.c b/drivers/staging/hv/hv_utils.c
> index 8f1d3ba..c0f57a1 100644
> --- a/drivers/staging/hv/hv_utils.c
> +++ b/drivers/staging/hv/hv_utils.c
> @@ -106,28 +106,45 @@ static void shutdown_onchannelcallback(void *context)
>  		orderly_poweroff(false);
>  }
>  
> -
>  /*
> - * Synchronize time with host after reboot, restore, etc.
> + * Set guest time to host UTC time.
>   */
> -static void adj_guesttime(u64 hosttime, u8 flags)
> +static inline void do_adj_guesttime(u64 hosttime)
>  {
>  	s64 host_tns;
>  	struct timespec host_ts;
> -	static s32 scnt = 50;
>  
>  	host_tns = (hosttime - WLTIMEDELTA) * 100;
>  	host_ts = ns_to_timespec(host_tns);
>  
> +	do_settimeofday(&host_ts);
> +
> +	return;
> +}
Just a couple of style nits.

return at the end of a void function() is unnecessary.
> +
> +/*
> + * Synchronize time with host after reboot, restore, etc.
> + *
> + * ICTIMESYNCFLAG_SYNC flag bit indicates reboot, restore events of the
VM.
> + * After reboot the flag ICTIMESYNCFLAG_SYNC is included in the first time
> + * message after the timesync channel is opened. Since the hv_utils module
is
> + * loaded after hv_vmbus, the first message is usually missed. The other
> + * thing is, systime is automatically set to emulated hardware clock which
may
> + * not be UTC time or in the same time zone. So, to override these
effects, we
> + * use the first 50 time samples for initial system time setting.
> + */
> +static inline void adj_guesttime(u64 hosttime, u8 flags)
> +{
> +	static s32 scnt = 50;
> +
>  	if ((flags & ICTIMESYNCFLAG_SYNC) != 0) {
> -		do_settimeofday(&host_ts);
> +		do_adj_guesttime(hosttime);
>  		return;
>  	}
>  
> -	if ((flags & ICTIMESYNCFLAG_SAMPLE) != 0 &&
> -	    scnt > 0) {
> +	if ((flags & ICTIMESYNCFLAG_SAMPLE) != 0 && scnt > 0) {
>  		scnt--;
> -		do_settimeofday(&host_ts);
> +		do_adj_guesttime(hosttime);
>  	}
>  
>  	return;
here too