On Wed, May 08, 2024 at 09:23:17AM GMT, Tvrtko Ursulin wrote:
On 07/05/2024 22:35, Lucas De Marchi wrote:
On Fri, Apr 26, 2024 at 11:47:37AM GMT, Tvrtko Ursulin wrote:
On 24/04/2024 00:56, Lucas De Marchi wrote:
Print the accumulated runtime for client when printing fdinfo.
Each time a query is done it first does 2 things:
1) loop through all the exec queues for the current client and
accumulate the runtime, per engine class. CTX_TIMESTAMP is used for
that, being read from the context image.
2) Read a "GPU timestamp" that can be used for considering "how much GPU
time has passed" and that has the same unit/refclock as the one
recording the runtime. RING_TIMESTAMP is used for that via MMIO.
Since for all current platforms RING_TIMESTAMP follows the same
refclock, just read it once, using any first engine.
This is exported to userspace as 2 numbers in fdinfo:
drm-cycles-<class>: <RUNTIME>
drm-total-cycles-<class>: <TIMESTAMP>
Userspace is expected to collect at least 2 samples, which allows to
know the client engine busyness as per:
RUNTIME1 - RUNTIME0
busyness = ---------------------
T1 - T0
Another thing to point out is that it's expected that userspace will
read any 2 samples every few seconds. Given the update frequency of the
counters involved and that CTX_TIMESTAMP is 32-bits, the counter for
each exec_queue can wrap around (assuming 100% utilization) after ~200s.
The wraparound is not perceived by userspace since it's just accumulated
for all the exec_queues in a 64-bit counter), but the measurement will
not be accurate if the samples are too far apart.
This could be mitigated by adding a workqueue to accumulate the counters
every so often, but it's additional complexity for something that is
done already by userspace every few seconds in tools like gputop (from
igt), htop, nvtop, etc with none of them really defaulting to 1 sample
per minute or more.
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
Documentation/gpu/drm-usage-stats.rst | 16 ++-
Documentation/gpu/xe/index.rst | 1 +
Documentation/gpu/xe/xe-drm-usage-stats.rst | 10 ++
drivers/gpu/drm/xe/xe_drm_client.c | 138 +++++++++++++++++++-
4 files changed, 162 insertions(+), 3 deletions(-)
create mode 100644 Documentation/gpu/xe/xe-drm-usage-stats.rst
diff --git a/Documentation/gpu/drm-usage-stats.rst
b/Documentation/gpu/drm-usage-stats.rst
index 6dc299343b48..421766289b78 100644
--- a/Documentation/gpu/drm-usage-stats.rst
+++ b/Documentation/gpu/drm-usage-stats.rst
@@ -112,6 +112,17 @@ larger value within a reasonable period.
Upon observing a value lower than what
was previously read, userspace is expected to stay with that
larger previous
value until a monotonic update is seen.
+- drm-total-cycles-<keystr>: <uint>
+
+Engine identifier string must be the same as the one specified in the
+drm-cycles-<keystr> tag and shall contain the total number
cycles for the given
+engine.
+
+This is a timestamp in GPU unspecified unit that matches the
update rate
+of drm-cycles-<keystr>. For drivers that implement this
interface, the engine
+utilization can be calculated entirely on the GPU clock domain, without
+considering the CPU sleep time between 2 samples.
Two opens.
1)
Do we need to explicity document that drm-total-cycles and
drm-maxfreq are mutually exclusive?
so userspace has a fallback mechanism to calculate utilization depending
on what keys are available?
No, to document all three at once do not make sense. Or at least are
not expected. Or you envisage someone might legitimately emit all
three? I don't see what would be the semantics. When we have
cycles+maxfreq the latter is in Hz. And when we have cycles+total then
it is unitless. All three?
I don't follow what you mean here. *cycles* is actually a unit.
The engine spent 10 cycles running this context (drm-cycles). In the
same period there were 100 cycles available (drm-total-cycles). Current
frequency is X MHz. Max frequency is Y MHz. For me all of them make
sense if one wants to mix them together. For xe it doesn't make sense
because the counter backing drm-cycles and drm-total-cycles is unrelated
to the engine frequency.
I can add something in the doc that we do not expected to see all of them
together until we see a usecase. Each driver may implement a subset.
2)
Should drm-total-cycles for now be documents as driver specific?
you mean to call it xe-total-cycles?
Yes but it is not an ask, just an open.
Ok, my opinion is that we shouldn't. Just like we have drm-cycles today
implemented by some drivers, but not all. I'd consider the drm-curfreq,
not documented in the drm layer as something to be fixed or migrated to
a driver-only interface (probably not possible anymore as it'd break the
uapi). Problem I see with turning it into xe-total-cycles, is that the
moment another driver decide to implement they will either have to use
xe- prefix or xe will need to start publishing both keys.
As said above, I can document that it's not expected to use both total
and maxfreq as it's currently the case.
I have added some more poeple in the cc who were involved with
driver fdinfo implementations if they will have an opinion.
I would say potentially yes, and promote it to common if more than
one driver would use it.
For instance I see panfrost has the driver specific drm-curfreq
(although isn't documenting it fully in panfrost.rst). And I have
to say it is somewhat questionable to expose the current frequency
per fdinfo per engine but not my call.
aren't all of Documentation/gpu/drm-usage-stats.rst optional that
driver may or may not implement? When you say driver-specific I'd think
more of the ones not using <drm> as prefix as e.g. amd-*.
I think drm-cycles + drm-total-cycles is just an alternative
implementation for engine utilization. Like drm-cycles + drm-maxfreq
already is an alternative to drm-engine and is not implemented by e.g.
amdgpu/i915.
I will submit a new version of the entire patch series to get the ball
rolling, but let's keep this open for now.
<...>
+static void show_runtime(struct drm_printer *p, struct drm_file *file)
+{
+ struct xe_file *xef = file->driver_priv;
+ struct xe_device *xe = xef->xe;
+ struct xe_gt *gt;
+ struct xe_hw_engine *hwe;
+ struct xe_exec_queue *q;
+ unsigned long i, id_hwe, id_gt,
capacity[XE_ENGINE_CLASS_MAX] = { };
+ u64 gpu_timestamp, engine_mask = 0;
+ bool gpu_stamp = false;
+
+ xe_pm_runtime_get(xe);
+
+ /* Accumulate all the exec queues from this client */
+ mutex_lock(&xef->exec_queue.lock);
+ xa_for_each(&xef->exec_queue.xa, i, q)
+ xe_exec_queue_update_runtime(q);
+ mutex_unlock(&xef->exec_queue.lock);
+
+
+ /* Calculate capacity of each engine class */
+ BUILD_BUG_ON(ARRAY_SIZE(class_to_mask) != XE_ENGINE_CLASS_MAX);
+ for_each_gt(gt, xe, id_gt)
+ engine_mask |= gt->info.engine_mask;
+ for (i = 0; i < XE_ENGINE_CLASS_MAX; i++)
+ capacity[i] = hweight64(engine_mask & class_to_mask[i]);
FWIW the above two loops are static so could store capacity in
struct xe_device.
yes, but just creating a cache in xe of something derived from gt is not
something to consider lightly. Particularly considering the small number
of xe->info.gt_count we have. For something that runs only when someone
cat the fdinfo, this doesn't seem terrible.
+
+ /*
+ * Iterate over all engines, printing the accumulated
+ * runtime for this client, per engine class
+ */
+ for_each_gt(gt, xe, id_gt) {
+ xe_force_wake_get(gt_to_fw(gt), XE_FW_GT);
+ for_each_hw_engine(hwe, gt, id_hwe) {
+ const char *class_name;
+
+ if (!capacity[hwe->class])
+ continue;
+
+ /*
+ * Use any (first) engine to have a timestamp to be
used every
+ * time
+ */
+ if (!gpu_stamp) {
+ gpu_timestamp = xe_hw_engine_read_timestamp(hwe);
+ gpu_stamp = true;
+ }
+
+ class_name = xe_hw_engine_class_to_str(hwe->class);
+
+ drm_printf(p, "drm-cycles-%s:\t%llu\n",
+ class_name, xef->runtime[hwe->class]);
+ drm_printf(p, "drm-total-cycles-%s:\t%llu\n",
+ class_name, gpu_timestamp);
+
+ if (capacity[hwe->class] > 1)
+ drm_printf(p, "drm-engine-capacity-%s:\t%lu\n",
+ class_name, capacity[hwe->class]);
+
+ /* engine class already handled, skip next iterations */
+ capacity[hwe->class] = 0;
+ }
+ xe_force_wake_put(gt_to_fw(gt), XE_FW_GT);
+ }
More FWIW and AFAICT, could just walk the "list" of classes
instead of
xe_force_wake_get() is per gt, so the alternative would be... loop
through the gts to get all forcewakes, loop through all engine
classes, loop
again through all gts to put the forcewake. And we also need to consider
that an engine class may not be available in all GTs... example:
vcs/vecs in MTL and later, so we need to track it globally across GTs
anyway.
Forcewake is only needed once for the gpu_timestamp, no? At least I
don't see any other potential hardware access in the loop. Hence I
thought if you could have a known engine to get the timestamp outside
the loop, you could then run a flat loop (over classes) avoiding the
per gt fw dance. Your choice ofc.
makes sense... I will try this and run some tests.
thanks
Lucas De Marchi
