In some IGT we have quite strict timing requirements that are trying to
measure workloads and not the latency of execution. For these, ksoftirqd
can cause quite a bit of mischief with long and unpredictable scheduling
delays, so lets explicitly flush the softirq tasklets via the
local_bh_enable() trick. This has to be done on_each_cpu() as the
tasklets when scheduled are local to a CPU.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Arjun Melkaveri <arjun.melkaveri@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_debugfs.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index aa35a59f1c7d..aa0da72878a6 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1429,6 +1429,7 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_perf_noa_delay_fops,
#define DROP_RESET_ACTIVE BIT(7)
#define DROP_RESET_SEQNO BIT(8)
#define DROP_RCU BIT(9)
+#define DROP_TASKLETS BIT(10)
#define DROP_ALL (DROP_UNBOUND | \
DROP_BOUND | \
DROP_RETIRE | \
@@ -1438,7 +1439,8 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_perf_noa_delay_fops,
DROP_IDLE | \
DROP_RESET_ACTIVE | \
DROP_RESET_SEQNO | \
- DROP_RCU)
+ DROP_RCU | \
+ DROP_TASKLETS)
static int
i915_drop_caches_get(void *data, u64 *val)
{
@@ -1476,6 +1478,21 @@ gt_drop_caches(struct intel_gt *gt, u64 val)
return 0;
}
+static void kick_softirq_tasklets(void *arg)
+{
+ /* Execute the softirq tasklets immediately */
+ local_bh_disable();
+ local_bh_enable();
+
+ /* Some tasklets may have queued others, so double check */
+ local_bh_disable();
+ local_bh_enable();
+
+ /* Third time's the charm. I don't think we recurse any deeper! */
+ local_bh_disable();
+ local_bh_enable();
+}
+
static int
i915_drop_caches_set(void *data, u64 val)
{
@@ -1485,6 +1502,9 @@ i915_drop_caches_set(void *data, u64 val)
DRM_DEBUG("Dropping caches: 0x%08llx [0x%08llx]\n",
val, val & DROP_ALL);
+ if (val & DROP_TASKLETS)
+ on_each_cpu(kick_softirq_tasklets, NULL, true);
+
ret = gt_drop_caches(&i915->gt, val);
if (ret)
return ret;
--
2.20.1
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