From: Jan Glauber <jglauber@redhat.com>
Date: Thu, 27 Mar 2008 17:26:05 +0100
Subject: [s390] FCP/SCSI write IO stagnates
Message-id: 1206635165.32695.7.camel@localhost.localdomain
O-Subject: [RHEL5.2 PATCH] s390: FCP/SCSI write IO stagnates
Bugzilla: 437099

Description:
============

Description: qdio / zfcp: slow database write IO to FCP/SCSI disk
Symptom:     Database write IO to FCP/SCSI disk getting caught steady.
             Running on LPAR database load times increase by more
             than factor 10x compared to ECKD disks.
Problem:     qdio tries to avoid adapter interrupts by exploiting
             a certain kind of polling state. When leaving this
             state, qdio may overlook an arrived buffer in a certain
             scenario. This scenario occurs only for zfcp-usage, not
             for qeth-usage.
Solution:    make sure qdio takes notice of additionally arriving.
             buffers in any cases.

Bugzilla
=========
BZ 437099
https://bugzilla.redhat.com/show_bug.cgi?id=437099

Upstream status of the patch:
=============================
git commit: e5fa443ea05f71b5253818890c6d32174cbab36f

Test status:
============
Tested by IBM to resolve the performance issue.

Please ack,

Jan

jglauber@redhat.com
jang@de.ibm.com

diff --git a/drivers/s390/cio/qdio.c b/drivers/s390/cio/qdio.c
index af13e3e..9b95742 100644
--- a/drivers/s390/cio/qdio.c
+++ b/drivers/s390/cio/qdio.c
@@ -1207,9 +1207,6 @@ tiqdio_is_inbound_q_done(struct qdio_q *q)
 
 	if (!no_used)
 		return 1;
-	if (!q->siga_sync && !irq->is_qebsm)
-		/* we'll check for more primed buffers in qeth_stop_polling */
-		return 0;
 	if (irq->is_qebsm) {
 		count = 1;
 		start_buf = q->first_to_check;