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;
On 06/17/2016 05:47 PM, Arnd Bergmann wrote:
- 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;
Does this patch introduce a 64-bit division? There might still be 32-bit users of this code.
Bart.
On Monday, June 20, 2016 3:54:06 PM CEST Bart Van Assche wrote:
On 06/17/2016 05:47 PM, Arnd Bergmann wrote:
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;
Does this patch introduce a 64-bit division? There might still be 32-bit users of this code.
No, both lport->boot_time and jiffies are 'unsigned long'.
Arnd
On 06/20/2016 04:48 PM, Arnd Bergmann wrote:
On Monday, June 20, 2016 3:54:06 PM CEST Bart Van Assche wrote:
On 06/17/2016 05:47 PM, Arnd Bergmann wrote:
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;
Does this patch introduce a 64-bit division? There might still be 32-bit users of this code.
No, both lport->boot_time and jiffies are 'unsigned long'.
Ah, you're right. Hence:
Reviewed-by: Bart Van Assche bart.vanassche@sandisk.com
"Arnd" == Arnd Bergmann arnd@arndb.de writes:
Arnd> The fc_get_host_stats() function contains a complex conversion Arnd> from jiffies to timespec to seconds. As we try to get rid of uses Arnd> of struct timespec, we can clean this up and replace it with a Arnd> simpler computation.
Arnd> Simply dividing the difference in jiffies by HZ is not only much Arnd> more efficient, it also avoids a problem that causes the Arnd> seconds_since_last_reset value to be incorrect if jiffies has Arnd> overrun since the 'boot_time' value was recorded.
Applied to 4.8/scsi-queue.