Re: [PATCH] i915/pmu: Wire GuC backend to per-client busyness

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On 14/06/2022 17:32, Umesh Nerlige Ramappa wrote:
On Tue, Jun 14, 2022 at 02:30:42PM +0100, Tvrtko Ursulin wrote:

On 14/06/2022 01:46, Nerlige Ramappa, Umesh wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>

GuC provides engine_id and last_switch_in ticks for an active context in the pphwsp. The context image provides a 32 bit total ticks which is the accumulated by the context (a.k.a. context[CTX_TIMESTAMP]). This information is used to
calculate the context busyness as follows:

If the engine_id is valid, then busyness is the sum of accumulated total ticks and active ticks. Active ticks is calculated with current gt time as reference.

If engine_id is invalid, busyness is equal to accumulated total ticks.

Since KMD (CPU) retrieves busyness data from 2 sources - GPU and GuC, a
potential race was highlighted in an earlier review that can lead to double accounting of busyness. While the solution to this is a wip, busyness is still
usable for platforms running GuC submission.

Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/intel_context.c       | 11 +++-
 drivers/gpu/drm/i915/gt/intel_context.h       |  6 +-
 drivers/gpu/drm/i915/gt/intel_context_types.h |  3 +
 drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h   |  5 ++
 .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 55 ++++++++++++++++++-
 drivers/gpu/drm/i915/i915_drm_client.c        |  6 +-
 6 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 4070cb5711d8..a49f313db911 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -576,16 +576,23 @@ void intel_context_bind_parent_child(struct intel_context *parent,
     child->parallel.parent = parent;
 }
-u64 intel_context_get_total_runtime_ns(const struct intel_context *ce)
+u64 intel_context_get_total_runtime_ns(struct intel_context *ce)
 {
     u64 total, active;
+    if (ce->ops->update_stats)
+        ce->ops->update_stats(ce);
+
     total = ce->stats.runtime.total;
     if (ce->ops->flags & COPS_RUNTIME_CYCLES)
         total *= ce->engine->gt->clock_period_ns;
     active = READ_ONCE(ce->stats.active);
-    if (active)
+    /*
+     * GuC backend returns the actual time the context was active, so skip
+     * the calculation here for GuC.
+     */
+    if (active && !intel_engine_uses_guc(ce->engine))

What is the point of looking at ce->stats.active in GuC mode? I see that guc_context_update_stats/__guc_context_update_clks touches it, but I can't spot that there is a purpose to it. This is the only conditional reading it but it is short-circuited in GuC case.

Also, since a GuC only vfunc (update_stats) has been added, I wonder why not just fork the whole runtime query (ce->get_total_runtime_ns). I think that would end up cleaner.

         active = intel_context_clock() - active;
     return total + active;

In case of GuC the active is used directly here since the active updated in update_stats is equal to the active time of the context already. I will look into separate vfunc.

Ah right, I misread something. But yes, I think a separate vfunc will look cleaner. Another option (instead of vfunc) is a similar flag to control the express the flavour of active?

diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
index b7d3214d2cdd..5fc7c19ab29b 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.h
+++ b/drivers/gpu/drm/i915/gt/intel_context.h
@@ -56,7 +56,7 @@ static inline bool intel_context_is_parent(struct intel_context *ce)
     return !!ce->parallel.number_children;
 }

snip

+static void __guc_context_update_clks(struct intel_context *ce)
+{
+    struct intel_guc *guc = ce_to_guc(ce);
+    struct intel_gt *gt = ce->engine->gt;
+    u32 *pphwsp, last_switch, engine_id;
+    u64 start_gt_clk = 0, active = 0;

No need to init these two.

+    unsigned long flags;
+    ktime_t unused;
+
+    spin_lock_irqsave(&guc->timestamp.lock, flags);
+
+    pphwsp = ((void *)ce->lrc_reg_state) - LRC_STATE_OFFSET;
+    last_switch = READ_ONCE(pphwsp[PPHWSP_GUC_CONTEXT_USAGE_STAMP_LO]);
+    engine_id = READ_ONCE(pphwsp[PPHWSP_GUC_CONTEXT_USAGE_ENGINE_ID]);
+
+    guc_update_pm_timestamp(guc, &unused);
+
+    if (engine_id != 0xffffffff && last_switch) {
+        start_gt_clk = READ_ONCE(ce->stats.runtime.start_gt_clk);
+        __extend_last_switch(guc, &start_gt_clk, last_switch);
+        active = intel_gt_clock_interval_to_ns(gt, guc->timestamp.gt_stamp - start_gt_clk);
+        WRITE_ONCE(ce->stats.runtime.start_gt_clk, start_gt_clk);
+        WRITE_ONCE(ce->stats.active, active);
+    } else {
+        lrc_update_runtime(ce);

Why is this called from here? Presumably it was called already from guc_context_unpin if here code things context is not active. Or will be called shortly, once context save is done.

guc_context_unpin is only called in the path of ce->sched_disable. The sched_disable is implemented in GuC (H2G message). Once the corresponding G2H response is received, the context is actually unpinned, eventually calling guc_context_unpin. Also the context may not necessarily be disabled after each context exit.

So if I understand correctly, lrc runtime is only updated if someone is reading the busyness and not as part of normal context state transitions?

Regards,

Tvrtko



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