ata: libata-eh: avoid unnecessary calls to ata_scsi_port_error_handler()

When handling SCSI command timeouts, if we had no actual command
timeouts (either because the command was a deferred qc or the completion
path won the race with ata_scsi_cmd_error_handler()), we do not need to
go through a port error handling, as there was in fact no errors at all.

Modify ata_scsi_cmd_error_handler() to return the number of commands
that timed out and use this return value in ata_scsi_error() to call
ata_scsi_port_error_handler() only if we had command timeouts, or if
the port EH has already been scheduled due to failed commands.
Otherwise, simply call scsi_eh_flush_done_q() to finish the completed
commands without running the full port error handling.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 72a22b6c968216d1f43ebe73b96d020ddb0ea5d5..12c6740398fa862123c2a640b55ee4359397df49 100644 (file)
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -560,21 +560,27 @@ void ata_scsi_error(struct Scsi_Host *host)
 {
        struct ata_port *ap = ata_shost_to_port(host);
        unsigned long flags;
+       int nr_timedout;
        LIST_HEAD(eh_work_q);
 
        spin_lock_irqsave(host->host_lock, flags);
        list_splice_init(&host->eh_cmd_q, &eh_work_q);
        spin_unlock_irqrestore(host->host_lock, flags);
 
-       ata_scsi_cmd_error_handler(host, ap, &eh_work_q);
-
-       /* If we timed raced normal completion and there is nothing to
-          recover nr_timedout == 0 why exactly are we doing error recovery ? */
-       ata_scsi_port_error_handler(host, ap);
+       /*
+        * First check what errors we got with ata_scsi_cmd_error_handler().
+        * If we had no command timeouts and EH is not scheduled for this port,
+        * meaning that we do not have any failed command, then there is no
+        * need to go through the full port error handling. We only need to
+        * flush the completed commands we have.
+        */
+       nr_timedout = ata_scsi_cmd_error_handler(host, ap, &eh_work_q);
+       if (nr_timedout || ata_port_eh_scheduled(ap))
+               ata_scsi_port_error_handler(host, ap);
+       else
+               scsi_eh_flush_done_q(&ap->eh_done_q);
 
-       /* finish or retry handled scmd's and clean up */
        WARN_ON(!list_empty(&eh_work_q));
-
 }
 
 /**
@@ -586,9 +592,11 @@ void ata_scsi_error(struct Scsi_Host *host)
  * process the given list of commands and return those finished to the
  * ap->eh_done_q.  This function is the first part of the libata error
  * handler which processes a given list of failed commands.
+ *
+ * Return the number of commands that timed out.
  */
-void ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap,
-                               struct list_head *eh_work_q)
+int ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap,
+                              struct list_head *eh_work_q)
 {
        int i;
        unsigned long flags;
@@ -678,6 +686,8 @@ void ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap,
        ap->eh_tries = ATA_EH_MAX_TRIES;
 
        spin_unlock_irqrestore(ap->lock, flags);
+
+       return nr_timedout;
 }
 EXPORT_SYMBOL(ata_scsi_cmd_error_handler);
 

diff --git a/include/linux/libata.h b/include/linux/libata.h
index db87c99e418915f3b809723dc39600ad2557e4a1..5c085ef4eda7b3e8dc03bda0da514a9409eeb73f 100644 (file)
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1225,7 +1225,8 @@ extern int ata_ncq_prio_enable(struct ata_port *ap, struct scsi_device *sdev,
 extern struct ata_device *ata_dev_pair(struct ata_device *adev);
 int ata_set_mode(struct ata_link *link, struct ata_device **r_failed_dev);
 extern void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap);
-extern void ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap, struct list_head *eh_q);
+int ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap,
+                              struct list_head *eh_q);
 
 /*
  * SATA specific code - drivers/ata/libata-sata.c