Hi Mike,
I got fed up with the large number of rejects I've seen from queuecommand
due to the CmdSN window closing on us.
So I put together a patch for dynamically adjusting shost->can_queue
depending on the number of rejects.
Purely as a proof-on-concept, but works out quite nicely.
I did on purpose _not_ calling the change_queue_depth callback
as this would induce quite some overhead here with very
little gain, as shost->can_queue seems to be more appropriate
here as we're deducing the number of commands for the host/target,
not the LUN.
Interesting though, both NetApp and MSA level out at around
64 commands. Maybe we should consider changing the default ...
Feedback welcome.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
[email protected] +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 0356e3d..a4d6eda 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -1592,7 +1743,7 @@ int iscsi_queuecommand(struct scsi_cmnd *sc, void
(*done)(struct scsi_cmnd *))
struct iscsi_cls_session *cls_session;
struct Scsi_Host *host;
struct iscsi_host *ihost;
- int reason = 0;
+ int reason = 0, adjust_qdepth = 0;
struct iscsi_session *session;
struct iscsi_conn *conn;
struct iscsi_task *task = NULL;
@@ -1684,27 +1835,53 @@ int iscsi_queuecommand(struct scsi_cmnd *sc, void
(*done)(struct scsi_cmnd *))
}
session->queued_cmdsn++;
+ if (session->reject_count < 20) {
+ adjust_qdepth = 1;
+ session->reject_count = 100;
+ } else {
+ session->reject_count--;
+ }
spin_unlock(&session->lock);
spin_lock(host->host_lock);
+ if (adjust_qdepth == 1) {
+ host->can_queue++;
+ iscsi_session_printk(KERN_INFO, session,
+ "adjusted queue depth to %u\n",
+ host->can_queue);
+ }
return 0;
prepd_reject:
sc->scsi_done = NULL;
iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
reject:
- spin_unlock(&session->lock);
ISCSI_DBG_SESSION(session, "cmd 0x%x rejected (%d)\n",
sc->cmnd[0], reason);
+
+ if (session->reject_count > 200) {
+ adjust_qdepth = -1;
+ session->reject_count = 100;
+ } else {
+ session->reject_count++;
+ }
+ spin_unlock(&session->lock);
spin_lock(host->host_lock);
+ if (adjust_qdepth == -1) {
+ host->can_queue--;
+ iscsi_session_printk(KERN_INFO, session,
+ "adjusted queue depth to %u\n",
+ host->can_queue);
+ }
return SCSI_MLQUEUE_TARGET_BUSY;
prepd_fault:
sc->scsi_done = NULL;
iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
fault:
- spin_unlock(&session->lock);
+ session->fault_count++;
ISCSI_DBG_SESSION(session, "iscsi: cmd 0x%x is not queued (%d)\n",
sc->cmnd[0], reason);
+ spin_unlock(&session->lock);
if (!scsi_bidi_cmnd(sc))
scsi_set_resid(sc, scsi_bufflen(sc));
else {
@@ -2793,6 +2982,7 @@ int iscsi_conn_start(struct iscsi_cls_conn *cls_conn)
conn->last_recv = jiffies;
conn->last_ping = jiffies;
+ session->reject_count = 100;
if (conn->recv_timeout && conn->ping_timeout)
mod_timer(&conn->transport_timer,
jiffies + (conn->recv_timeout * HZ));
diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
index 61afeb5..b006a32 100644
--- a/include/scsi/libiscsi.h
+++ b/include/scsi/libiscsi.h
@@ -298,6 +303,7 @@ struct iscsi_session {
* - r2tpool */
int state; /* session state */
int age; /* counts session re-opens */
+ unsigned long reject_count; /* counts cmd rejects */
int scsi_cmds_max; /* max scsi commands */
int cmds_max; /* size of cmds array */
