[SCSI] Set the minimum valid value of 'eh_deadline' as 0

The former minimum valid value of 'eh_deadline' is 1s, which means
the earliest occasion to shorten EH is 1 second later since a
command is failed or timed out. But if we want to skip EH steps
ASAP, we have to wait until the first EH step is finished. If the
duration of the first EH step is long, this waiting time is
excruciating. So, it is necessary to accept 0 as the minimum valid
value for 'eh_deadline'.

According to my test, with Hannes' patchset 'New EH command timeout
handler' as well, the minimum IO time is improved from 73s
(eh_deadline = 1) to 43s(eh_deadline = 0) when commands are timed
out by disabling RSCN and target port.

Signed-off-by: Ren Mingxin <renmx@cn.fujitsu.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 25 insertions, 11 deletions

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 8ff62c26a41c..9117d0bf408e 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -287,7 +287,9 @@ show_shost_eh_deadline(struct device *dev,
 {
         struct Scsi_Host *shost = class_to_shost(dev);
 
-        return sprintf(buf, "%d\n", shost->eh_deadline / HZ);
+        if (shost->eh_deadline == -1)
+                return snprintf(buf, strlen("off") + 2, "off\n");
+        return sprintf(buf, "%u\n", shost->eh_deadline / HZ);
 }
 
 static ssize_t
@@ -296,22 +298,34 @@ store_shost_eh_deadline(struct device *dev, struct device_attribute *attr,
 {
         struct Scsi_Host *shost = class_to_shost(dev);
         int ret = -EINVAL;
-        int deadline;
-        unsigned long flags;
+        unsigned long deadline, flags;
 
         if (shost->transportt && shost->transportt->eh_strategy_handler)
                 return ret;
 
-        if (sscanf(buf, "%d\n", &deadline) == 1) {
-                spin_lock_irqsave(shost->host_lock, flags);
-                if (scsi_host_in_recovery(shost))
-                        ret = -EBUSY;
-                else {
+        if (!strncmp(buf, "off", strlen("off")))
+                deadline = -1;
+        else {
+                ret = kstrtoul(buf, 10, &deadline);
+                if (ret)
+                        return ret;
+                if (deadline * HZ > UINT_MAX)
+                        return -EINVAL;
+        }
+
+        spin_lock_irqsave(shost->host_lock, flags);
+        if (scsi_host_in_recovery(shost))
+                ret = -EBUSY;
+        else {
+                if (deadline == -1)
+                        shost->eh_deadline = -1;
+                else
                         shost->eh_deadline = deadline * HZ;
-                        ret = count;
-                }
-                spin_unlock_irqrestore(shost->host_lock, flags);
+
+                ret = count;
         }
+        spin_unlock_irqrestore(shost->host_lock, flags);
+
         return ret;
 }