[PATCH v3 39/46] perf/x86/intel/cmt: add max_recycle_threshold sysfs attribute

[David Carrillo-Cisneros <davidcc@google.com>]

Expose max_recycle_threshold as a configurable sysfs attribute of
intel_cmt pmu. max_recycle_threshold determines the maximum dirty
threshold for rmids with no zero occupancy.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 arch/x86/events/intel/cmt.c | 57 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/arch/x86/events/intel/cmt.c b/arch/x86/events/intel/cmt.c
index 649eb5f..05803a8 100644
--- a/arch/x86/events/intel/cmt.c
+++ b/arch/x86/events/intel/cmt.c
@@ -61,6 +61,7 @@ static struct pkg_data **cmt_pkgs_data;
  * @__cmt_pre_mon_slice: Min time a monr is monitored before being readable.
  * @__cmt_min_mon_slice: Min time a monr stays monitored after becoming
  *                       readable.
+ * @__cmt_max_threshold: Max bytes of error due to reusing dirty rmids.
  */
 #define CMT_DEFAULT_PRE_MON_SLICE 2000		/* ms */
 static u64 __cmt_pre_mon_slice;
@@ -68,6 +69,7 @@ static u64 __cmt_pre_mon_slice;
 #define CMT_DEFAULT_MIN_MON_SLICE 5000		/* ms */
 static u64 __cmt_min_mon_slice;
 
+static unsigned int __cmt_max_threshold;	/* bytes */
 
 /*
  * If @pkgd == NULL, return first online, pkg_data in cmt_pkgs_data.
@@ -1831,9 +1833,54 @@ static struct attribute_group intel_cmt_format_group = {
 	.attrs = intel_cmt_formats_attr,
 };
 
+static ssize_t max_recycle_threshold_show(struct device *dev,
+				struct device_attribute *attr, char *page)
+{
+	ssize_t rv;
+
+	mutex_lock(&cmt_mutex);
+	rv = snprintf(page, PAGE_SIZE - 1, "%u\n",
+		      READ_ONCE(__cmt_max_threshold));
+
+	mutex_unlock(&cmt_mutex);
+	return rv;
+}
+
+static ssize_t max_recycle_threshold_store(struct device *dev,
+					   struct device_attribute *attr,
+					   const char *buf, size_t count)
+{
+	unsigned int bytes;
+	int err;
+
+	err = kstrtouint(buf, 0, &bytes);
+	if (err)
+		return err;
+
+	mutex_lock(&cmt_mutex);
+	monr_hrchy_acquire_mutexes();
+	WRITE_ONCE(__cmt_max_threshold, bytes);
+	monr_hrchy_release_mutexes();
+	mutex_unlock(&cmt_mutex);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(max_recycle_threshold);
+
+static struct attribute *intel_cmt_attrs[] = {
+	&dev_attr_max_recycle_threshold.attr,
+	NULL,
+};
+
+static const struct attribute_group intel_cmt_group = {
+	.attrs = intel_cmt_attrs,
+};
+
 static const struct attribute_group *intel_cmt_attr_groups[] = {
 	&intel_cmt_events_group,
 	&intel_cmt_format_group,
+	&intel_cmt_group,
 	NULL,
 };
 
@@ -2270,6 +2317,16 @@ static int __init cmt_start(void)
 	if (err)
 		goto rm_prep;
 
+	/*
+	 * A reasonable default upper limit on the max threshold is half of
+	 * the number of lines tagged per RMID if all RMIDs had the same
+	 * number of lines tagged in the LLC.
+	 *
+	 * For a 35MB LLC and 56 RMIDs, this is ~0.9% of the LLC or 320 KBs.
+	 */
+	__cmt_max_threshold = boot_cpu_data.x86_cache_size * 1024 /
+			(2 * (__min_max_rmid + 1));
+
 	snprintf(scale, sizeof(scale), "%u", cmt_l3_scale);
 	str = kstrdup(scale, GFP_KERNEL);
 	if (!str) {
-- 
2.8.0.rc3.226.g39d4020