[PATCH 13/19] s390/dasd: Add full_track_bias to control fulltrack write mode

@@ -1630,6 +1630,44 @@ dasd_expires_store(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR(expires, 0644, dasd_expires_show, dasd_expires_store);
 
+/* ESE fulltrack write aggressiveness knob (0..100, see DASD_FT_BIAS_*) */
+static ssize_t
+full_track_bias_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct dasd_device *device;
+	int len;
+
+	device = dasd_device_from_cdev(to_ccwdev(dev));
+	if (IS_ERR(device))
+		return -ENODEV;
+	len = sysfs_emit(buf, "%u\n", device->ft_bias);
+	dasd_put_device(device);
+	return len;
+}
+
+static ssize_t full_track_bias_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct dasd_device *device;
+	unsigned int val;
+
+	if (kstrtouint(buf, 0, &val) || val > DASD_FT_BIAS_MAX)
+		return -EINVAL;
+
+	device = dasd_device_from_cdev(to_ccwdev(dev));
+	if (IS_ERR(device))
+		return -ENODEV;
+
+	device->ft_bias = val;
+	device->fulltrack = val ? 1 : 0;
+
+	dasd_put_device(device);
+	return count;
+}
+
+static DEVICE_ATTR_RW(full_track_bias);
+
 static ssize_t
 dasd_retries_show(struct device *dev, struct device_attribute *attr, char *buf)
 {

@@ -2425,6 +2463,7 @@ static struct attribute * dasd_attrs[] = {
 	&dev_attr_erplog.attr,
 	&dev_attr_failfast.attr,
 	&dev_attr_expires.attr,
+	&dev_attr_full_track_bias.attr,
 	&dev_attr_retries.attr,
 	&dev_attr_timeout.attr,
 	&dev_attr_reservation_policy.attr,

@@ -48,6 +48,18 @@
 MODULE_DESCRIPTION("S/390 DASD ECKD Disks device driver");
 MODULE_LICENSE("GPL");
 
+/*
+ * Default full-track write bias applied to every ESE volume at online time;
+ * individual volumes can be re-tuned afterwards through their per-device
+ * full_track_bias sysfs attribute. 0 disables full-track writes, 100 always
+ * uses them, 50 (the default) enables the adaptive heuristic. Values above
+ * DASD_FT_BIAS_MAX are capped when applied.
+ */
+static unsigned int full_track_bias = DASD_FT_BIAS_DEFAULT;
+module_param(full_track_bias, uint, 0644);
+MODULE_PARM_DESC(full_track_bias,
+		 "Default ESE full-track write bias 0..100 (0=off, 1..99=adaptive, 100=always)");
+
 static struct dasd_discipline dasd_eckd_discipline;
 
 /* The ccw bus type uses this table to find devices that it sends to

@@ -2149,6 +2161,11 @@ dasd_eckd_check_characteristics(struct dasd_device *device)
 	device->path_interval = DASD_ECKD_PATH_INTERVAL;
 	device->aq_timeouts = DASD_RETRIES_MAX;
 
+	/* default ESE fulltrack write aggressiveness from the module parameter */
+	device->ft_bias = min_t(unsigned int, full_track_bias, DASD_FT_BIAS_MAX);
+	/* only the "always" endpoint forces fulltrack unconditionally here */
+	device->fulltrack = (device->ft_bias >= DASD_FT_BIAS_MAX) ? 1 : 0;
+
 	if (private->conf.gneq) {
 		value = 1;
 		for (i = 0; i < private->conf.gneq->timeout.value; i++)

@@ -5204,11 +5221,20 @@ static struct dasd_ccw_req *dasd_eckd_build_cp(struct dasd_device *startdev,
 		/* do nothing, just fall through to the cmd mode single case */
 	} else if ((data_size <= private->fcx_max_data)
 		   && (fcx_multitrack || (first_trk == last_trk))) {
-		cqr = dasd_eckd_build_cp_tpm_track(startdev, block, req,
-						    first_rec, last_rec,
-						    first_trk, last_trk,
-						    first_offs, last_offs,
-						    blk_per_trk, blksize);
+		if (!first_offs && (last_offs + 1 == blk_per_trk) &&
+		    rq_data_dir(req) == WRITE && basedev->fulltrack) {
+			cqr = dasd_eckd_build_cp_tpm_writefulltrack(startdev, block, req,
+								    first_rec, last_rec,
+								    first_trk, last_trk,
+								    first_offs, last_offs,
+								    blk_per_trk, blksize, NULL);
+		} else {
+			cqr = dasd_eckd_build_cp_tpm_track(startdev, block, req,
+							   first_rec, last_rec,
+							   first_trk, last_trk,
+							   first_offs, last_offs,
+							   blk_per_trk, blksize);
+		}
 		if (IS_ERR(cqr) && (PTR_ERR(cqr) != -EAGAIN) &&
 		    (PTR_ERR(cqr) != -ENOMEM))
 			cqr = NULL;

@@ -629,6 +629,10 @@ struct dasd_device {
 	struct dasd_copy_relation *copy;
 	unsigned long aq_mask;
 	unsigned int aq_timeouts;
+
+	/* ESE fulltrack write control (see full_track_bias sysfs attribute) */
+	unsigned int ft_bias;	/* aggressiveness 0..100: 0=off, 100=always */
+	unsigned int fulltrack;	/* internal: use WRITE_FULL_TRACK for aligned writes */
 };
 
 struct dasd_block {

@@ -686,6 +690,20 @@ struct dasd_queue {
 #define DASD_STOPPED_PPRC    32        /* PPRC swap */
 #define DASD_STOPPED_NOSPC   128       /* no space left */
 
+/*
+ * ESE fulltrack write aggressiveness (full_track_bias sysfs attribute), 0..100:
+ *   0   - never use proactively WRITE_FULL_TRACK
+ *   100 - always use proactively WRITE_FULL_TRACK, no probing
+ *   1..99 - adaptive; higher means switch to ft more eagerly
+ * WRITE_FULL_TRACK has an advantage on sparse formatted ESE devices
+ * but it has an overall penalty for maximum throughput for fully
+ * formatted devices.
+ * The default of 50 tries to balance both and do some probing in between
+ * to choose the best mode for default IO.
+ */
+#define DASD_FT_BIAS_MAX	100
+#define DASD_FT_BIAS_DEFAULT	50
+
 /* per device flags */
 #define DASD_FLAG_OFFLINE	3	/* device is in offline processing */
 #define DASD_FLAG_EER_SNSS	4	/* A SNSS is required */