[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, 13 insertions, 4 deletions

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index c3ab093dd8a7..f28ea070d3df 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -319,11 +319,11 @@ static void scsi_host_dev_release(struct device *dev)
         kfree(shost);
 }
 
-static unsigned int shost_eh_deadline;
+static int shost_eh_deadline = -1;
 
-module_param_named(eh_deadline, shost_eh_deadline, uint, S_IRUGO|S_IWUSR);
+module_param_named(eh_deadline, shost_eh_deadline, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(eh_deadline,
-                 "SCSI EH timeout in seconds (should be between 1 and 2^32-1)");
+                 "SCSI EH timeout in seconds (should be between 0 and 2^31-1)");
 
 static struct device_type scsi_host_type = {
         .name =         "scsi_host",
@@ -396,9 +396,18 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
         shost->unchecked_isa_dma = sht->unchecked_isa_dma;
         shost->use_clustering = sht->use_clustering;
         shost->ordered_tag = sht->ordered_tag;
-        shost->eh_deadline = shost_eh_deadline * HZ;
         shost->no_write_same = sht->no_write_same;
 
+        if (shost_eh_deadline == -1)
+                shost->eh_deadline = -1;
+        else if ((ulong) shost_eh_deadline * HZ > INT_MAX) {
+                shost_printk(KERN_WARNING, shost,
+                             "eh_deadline %u too large, setting to %u\n",
+                             shost_eh_deadline, INT_MAX / HZ);
+                shost->eh_deadline = INT_MAX;
+        } else
+                shost->eh_deadline = shost_eh_deadline * HZ;
+
         if (sht->supported_mode == MODE_UNKNOWN)
                 /* means we didn't set it ... default to INITIATOR */
                 shost->active_mode = MODE_INITIATOR;