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[PATCH] scsi: libfc: fix seconds_since_last_reset calculation

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The fc_get_host_stats() function contains a complex conversion
from jiffies to timespec to seconds. As we try to get rid of
uses of struct timespec, we can clean this up and replace it
with a simpler computation.

Simply dividing the difference in jiffies by HZ is not only
much more efficient, it also avoids a problem that causes the
seconds_since_last_reset value to be incorrect if jiffies has
overrun since the 'boot_time' value was recorded.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/scsi/libfc/fc_lport.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/scsi/libfc/fc_lport.c b/drivers/scsi/libfc/fc_lport.c
index e01a29863c38..99c6d9251404 100644
--- a/drivers/scsi/libfc/fc_lport.c
+++ b/drivers/scsi/libfc/fc_lport.c
@@ -301,7 +301,6 @@ struct fc_host_statistics *fc_get_host_stats(struct Scsi_Host *shost)
 {
 	struct fc_host_statistics *fc_stats;
 	struct fc_lport *lport = shost_priv(shost);
-	struct timespec v0, v1;
 	unsigned int cpu;
 	u64 fcp_in_bytes = 0;
 	u64 fcp_out_bytes = 0;
@@ -309,9 +308,7 @@ struct fc_host_statistics *fc_get_host_stats(struct Scsi_Host *shost)
 	fc_stats = &lport->host_stats;
 	memset(fc_stats, 0, sizeof(struct fc_host_statistics));
 
-	jiffies_to_timespec(jiffies, &v0);
-	jiffies_to_timespec(lport->boot_time, &v1);
-	fc_stats->seconds_since_last_reset = (v0.tv_sec - v1.tv_sec);
+	fc_stats->seconds_since_last_reset = (lport->boot_time - jiffies) / HZ;
 
 	for_each_possible_cpu(cpu) {
 		struct fc_stats *stats;
-- 
2.9.0

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[PATCH] scsi: libfc: fix seconds_since_last_reset calculation Arnd Bergmann <arnd@arndb.de> - 2016-06-17 17:50 +0200
  Re: [PATCH] scsi: libfc: fix seconds_since_last_reset calculation Arnd Bergmann <arnd@arndb.de> - 2016-06-20 16:50 +0200
  Re: [PATCH] scsi: libfc: fix seconds_since_last_reset calculation "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-06-21 04:10 +0200

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