[PATCH] scsi: libfc: fix seconds_since_last_reset calculation

From: Arnd Bergmann
Date: Fri Jun 17 2016 - 11:46:19 EST


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@xxxxxxxx>
---
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