dmaengine: idxd: add knob for enqcmds retries

Add a sysfs knob to allow tuning of retries for the kernel ENQCMDS
descriptor submission. While on host, it is not as likely that ENQCMDS
return busy during normal operations due to the driver controlling the
number of descriptors allocated for submission. However, when the driver is
operating as a guest driver, the chance of retry goes up significantly due
to sharing a wq with multiple VMs. A default value is provided with the
system admin being able to tune the value on a per WQ basis.

Suggested-by: Sanjay Kumar <sanjay.k.kumar@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/163820629464.2702134.7577370098568297574.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/dma/idxd/sysfs.c b/drivers/dma/idxd/sysfs.c
index 90857e776273..c0fec88ff6c1 100644
--- a/drivers/dma/idxd/sysfs.c
+++ b/drivers/dma/idxd/sysfs.c
@@ -945,6 +945,41 @@ static ssize_t wq_occupancy_show(struct device *dev, struct device_attribute *at
 static struct device_attribute dev_attr_wq_occupancy =
 		__ATTR(occupancy, 0444, wq_occupancy_show, NULL);
 
+static ssize_t wq_enqcmds_retries_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct idxd_wq *wq = confdev_to_wq(dev);
+
+	if (wq_dedicated(wq))
+		return -EOPNOTSUPP;
+
+	return sysfs_emit(buf, "%u\n", wq->enqcmds_retries);
+}
+
+static ssize_t wq_enqcmds_retries_store(struct device *dev, struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct idxd_wq *wq = confdev_to_wq(dev);
+	int rc;
+	unsigned int retries;
+
+	if (wq_dedicated(wq))
+		return -EOPNOTSUPP;
+
+	rc = kstrtouint(buf, 10, &retries);
+	if (rc < 0)
+		return rc;
+
+	if (retries > IDXD_ENQCMDS_MAX_RETRIES)
+		retries = IDXD_ENQCMDS_MAX_RETRIES;
+
+	wq->enqcmds_retries = retries;
+	return count;
+}
+
+static struct device_attribute dev_attr_wq_enqcmds_retries =
+		__ATTR(enqcmds_retries, 0644, wq_enqcmds_retries_show, wq_enqcmds_retries_store);
+
 static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_clients.attr,
 	&dev_attr_wq_state.attr,
@@ -961,6 +996,7 @@ static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_max_batch_size.attr,
 	&dev_attr_wq_ats_disable.attr,
 	&dev_attr_wq_occupancy.attr,
+	&dev_attr_wq_enqcmds_retries.attr,
 	NULL,
 };