Re: [Intel-gfx] [RFC PATCH 2/2] Fix per client busyness locking

Umesh Nerlige Ramappa
2022-08-31T22:46:13Z

On Wed, Aug 31, 2022 at 12:33:55PM -0700, Ashutosh Dixit wrote:
>1. Do all ce->stats updates and reads under guc->timestamp.lock

Other than the question about READ_ONCE/WRITE_ONCE, I am not sure I
understand what's broken in the locking logic here. Can you please add
some description? thanks

>2. Pin context image before reading
>3. Merge __guc_context_update_clks and guc_context_update_stats into a
> single function
>4. Call lrc_update_runtime() unconditionally in guc_context_update_stats
>5. Seems no need to update ce->stats.active with this approach
>
>Some of the above steps may not be correct or complete but the idea is to
>discuss/improve the original patch.
>
>Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
>---
> drivers/gpu/drm/i915/gt/intel_context.c | 2 +-
> drivers/gpu/drm/i915/gt/intel_context_types.h | 2 +-
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 41 ++++++++++---------
> 3 files changed, 24 insertions(+), 21 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
>index e2d70a9fdac0..c004f676de27 100644
>--- a/drivers/gpu/drm/i915/gt/intel_context.c
>+++ b/drivers/gpu/drm/i915/gt/intel_context.c
>@@ -581,7 +581,7 @@ u64 intel_context_get_total_runtime_ns(struct intel_context *ce)
> u64 total, active;
>
> if (ce->ops->update_stats)
>- ce->ops->update_stats(ce);
>+ return ce->ops->update_stats(ce);

This is an improvement that we can add and eventually, we can make this
a GuC specific vfunc. Doing so may also remove the
COPS_RUNTIME_ACTIVE_TOTAL option that I added to GuC specific context
ops.

>
> total = ce->stats.runtime.total;
> if (ce->ops->flags & COPS_RUNTIME_CYCLES)
>diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
>index f7ff4c7d81c7..699435bfff99 100644
>--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
>+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
>@@ -59,7 +59,7 @@ struct intel_context_ops {
>
> void (*sched_disable)(struct intel_context *ce);
>
>- void (*update_stats)(struct intel_context *ce);
>+ u64 (*update_stats)(struct intel_context *ce);
>
> void (*reset)(struct intel_context *ce);
> void (*destroy)(struct kref *kref);
>diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>index bee8cf10f749..40d0edaf2e0a 100644
>--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>@@ -1376,7 +1376,6 @@ static void __update_guc_busyness_stats(struct intel_guc *guc)
> spin_unlock_irqrestore(&guc->timestamp.lock, flags);
> }
>
>-static void __guc_context_update_clks(struct intel_context *ce);
> static void guc_timestamp_ping(struct work_struct *wrk)
> {
> struct intel_guc *guc = container_of(wrk, typeof(*guc),
>@@ -1401,7 +1400,8 @@ static void guc_timestamp_ping(struct work_struct *wrk)
>
> /* adjust context stats for overflow */
> xa_for_each(&guc->context_lookup, index, ce)
>- __guc_context_update_clks(ce);
>+ if (ce->ops->update_stats)
>+ ce->ops->update_stats(ce);

context pinning logic needs to be separated for this (ping) path vs. the
query path - intel_context_get_total_runtime_ns().
>
> intel_gt_reset_unlock(gt, srcu);
>
>@@ -1476,17 +1476,21 @@ void intel_guc_busyness_unpark(struct intel_gt *gt)
> guc->timestamp.ping_delay);
> }
>
>-static void __guc_context_update_clks(struct intel_context *ce)
>+static u64 guc_context_update_stats(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, active;
> unsigned long flags;
>+ u64 total, active = 0;
> ktime_t unused;
>
>+ intel_context_pin(ce);

intel_context_pin can sleep and we are not allowed to sleep in this path
- intel_context_get_total_runtime_ns(), however we can sleep in the ping
worker path, so ideally we want to separate it out for the 2 paths.

> spin_lock_irqsave(&guc->timestamp.lock, flags);
>
>+ lrc_update_runtime(ce);
>+ total = ce->stats.runtime.total;

For long running contexts and frequenct queries, calling this ^ when a
context is active does not add value. I would just call it in the else
like before.

>+
> /*
> * GPU updates ce->lrc_reg_state[CTX_TIMESTAMP] when context is switched
> * out, however GuC updates PPHWSP offsets below. Hence KMD (CPU)
>@@ -1502,27 +1506,26 @@ static void __guc_context_update_clks(struct intel_context *ce)
> 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);
>+ __extend_last_switch(guc, &ce->stats.runtime.start_gt_clk, last_switch);
>+ active = intel_gt_clock_interval_to_ns(gt,
>+ guc->timestamp.gt_stamp - ce->stats.runtime.start_gt_clk);

Makes sense. Earlier it was a rmw, now it's just a write to
ce->stats.runtime.start_gt_clk.

> }
>
> spin_unlock_irqrestore(&guc->timestamp.lock, flags);
>+ intel_context_unpin(ce);
>+
>+ return total + active;

return ce->stats.runtime.total + active;

and then drop the local copy of total by bringing back the else{}.

> }
>
>-static void guc_context_update_stats(struct intel_context *ce)
>+void lrc_update_runtime_locked(struct intel_context *ce)
> {
>- if (!intel_context_pin_if_active(ce)) {
>- WRITE_ONCE(ce->stats.runtime.start_gt_clk, 0);
>- WRITE_ONCE(ce->stats.active, 0);
>- return;
>- }
>+ struct intel_guc *guc = ce_to_guc(ce);
>+ unsigned long flags;
>
>- __guc_context_update_clks(ce);
>+ intel_context_pin(ce);
>+ spin_lock_irqsave(&guc->timestamp.lock, flags);
>+ lrc_update_runtime(ce);
>+ spin_unlock_irqrestore(&guc->timestamp.lock, flags);
> intel_context_unpin(ce);

From where lrc_update_runtime_locked is being called, I would assume
that the context is already pinned (until unpin_guc_id is called).

Thanks,
Umesh

> }
>
>@@ -2780,7 +2783,7 @@ static void guc_context_unpin(struct intel_context *ce)
> {
> struct intel_guc *guc = ce_to_guc(ce);
>
>- lrc_update_runtime(ce);
>+ lrc_update_runtime_locked(ce);
> unpin_guc_id(guc, ce);
> lrc_unpin(ce);
>
>--
>2.34.1
>