Quoting Tomasz Lis (2018-03-27 16:17:59)
> The patch adds support of preempt-to-idle requesting by setting a proper
> bit within Execlist Control Register, and receiving preemption result from
> Context Status Buffer.
>
> Preemption in previous gens required a special batch buffer to be executed,
> so the Command Streamer never preempted to idle directly. In Icelake it is
> possible, as there is a hardware mechanism to inform the kernel about
> status of the preemption request.
>
> This patch does not cover using the new preemption mechanism when GuC is
> active.
>
> Bspec: 18922
> Signed-off-by: Tomasz Lis <tomasz.lis@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 2 ++
> drivers/gpu/drm/i915/i915_pci.c | 3 ++-
> drivers/gpu/drm/i915/intel_device_info.h | 1 +
> drivers/gpu/drm/i915/intel_lrc.c | 45 +++++++++++++++++++++++++++-----
> drivers/gpu/drm/i915/intel_lrc.h | 1 +
> 5 files changed, 45 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 800230b..c32580b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2514,6 +2514,8 @@ intel_info(const struct drm_i915_private *dev_priv)
> ((dev_priv)->info.has_logical_ring_elsq)
> #define HAS_LOGICAL_RING_PREEMPTION(dev_priv) \
> ((dev_priv)->info.has_logical_ring_preemption)
> +#define HAS_HW_PREEMPT_TO_IDLE(dev_priv) \
> + ((dev_priv)->info.has_hw_preempt_to_idle)
>
> #define HAS_EXECLISTS(dev_priv) HAS_LOGICAL_RING_CONTEXTS(dev_priv)
>
> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> index 4364922..66b6700 100644
> --- a/drivers/gpu/drm/i915/i915_pci.c
> +++ b/drivers/gpu/drm/i915/i915_pci.c
> @@ -595,7 +595,8 @@ static const struct intel_device_info intel_cannonlake_info = {
> GEN(11), \
> .ddb_size = 2048, \
> .has_csr = 0, \
> - .has_logical_ring_elsq = 1
> + .has_logical_ring_elsq = 1, \
> + .has_hw_preempt_to_idle = 1
>
> static const struct intel_device_info intel_icelake_11_info = {
> GEN11_FEATURES,
> diff --git a/drivers/gpu/drm/i915/intel_device_info.h b/drivers/gpu/drm/i915/intel_device_info.h
> index 933e316..4eb97b5 100644
> --- a/drivers/gpu/drm/i915/intel_device_info.h
> +++ b/drivers/gpu/drm/i915/intel_device_info.h
> @@ -98,6 +98,7 @@ enum intel_platform {
> func(has_logical_ring_contexts); \
> func(has_logical_ring_elsq); \
> func(has_logical_ring_preemption); \
> + func(has_hw_preempt_to_idle); \
> func(has_overlay); \
> func(has_pooled_eu); \
> func(has_psr); \
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index ba7f783..1a22de4 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -153,6 +153,7 @@
> #define GEN8_CTX_STATUS_ACTIVE_IDLE (1 << 3)
> #define GEN8_CTX_STATUS_COMPLETE (1 << 4)
> #define GEN8_CTX_STATUS_LITE_RESTORE (1 << 15)
> +#define GEN11_CTX_STATUS_PREEMPT_IDLE (1 << 29)
>
> #define GEN8_CTX_STATUS_COMPLETED_MASK \
> (GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)
> @@ -183,7 +184,9 @@ static inline bool need_preempt(const struct intel_engine_cs *engine,
> const struct i915_request *last,
> int prio)
> {
> - return engine->i915->preempt_context && prio > max(rq_prio(last), 0);
> + return (engine->i915->preempt_context ||
> + HAS_HW_PREEMPT_TO_IDLE(engine->i915)) &&
Well, you haven't actually disabled allocating the preempt_context so...
But at any rate, making this an engine->flag would eliminate one pointer
dance.
> + prio > max(rq_prio(last), 0);
> }
>
> /**
> @@ -535,6 +538,25 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
> execlists_set_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT);
> }
>
> +static void gen11_preempt_to_idle(struct intel_engine_cs *engine)
> +{
> + struct intel_engine_execlists *execlists = &engine->execlists;
> +
> + GEM_TRACE("%s\n", engine->name);
> +
> + /*
> + * hardware which HAS_HW_PREEMPT_TO_IDLE(), always also
> + * HAS_LOGICAL_RING_ELSQ(), so we can assume ctrl_reg is set
> + */
> + GEM_BUG_ON(execlists->ctrl_reg != NULL);
> +
> + /* trigger preemption to idle */
> + writel(EL_CTRL_PREEMPT_TO_IDLE, execlists->ctrl_reg);
Future plans? Because just inserting the branch into the setter of
inject_preempt_context() resolves a lot of conflicts with other work.
> @@ -962,10 +987,13 @@ static void execlists_submission_tasklet(unsigned long data)
> status, buf[2*head + 1],
> execlists->active);
>
> - if (status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
> - GEN8_CTX_STATUS_PREEMPTED))
> + /* Check if switched to active or preempted to active */
> + if ((status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
> + GEN8_CTX_STATUS_PREEMPTED)) &&
> + !(status & GEN11_CTX_STATUS_PREEMPT_IDLE))
Setting HWACK here is harmless as it gets cleared again. Unless, there
is some oddity in the code flow.
> execlists_set_active(execlists,
> EXECLISTS_ACTIVE_HWACK);
> +
> if (status & GEN8_CTX_STATUS_ACTIVE_IDLE)
> execlists_clear_active(execlists,
> EXECLISTS_ACTIVE_HWACK);
> @@ -976,8 +1004,13 @@ static void execlists_submission_tasklet(unsigned long data)
> /* We should never get a COMPLETED | IDLE_ACTIVE! */
> GEM_BUG_ON(status & GEN8_CTX_STATUS_IDLE_ACTIVE);
>
> - if (status & GEN8_CTX_STATUS_COMPLETE &&
> - buf[2*head + 1] == execlists->preempt_complete_status) {
> + /*
> + * Check if preempted to real idle, either directly or
> + * the preemptive context already finished executing
> + */
> + if ((status & GEN11_CTX_STATUS_PREEMPT_IDLE) ||
> + (status & GEN8_CTX_STATUS_COMPLETE &&
> + buf[2*head + 1] == execlists->preempt_complete_status)) {
> GEM_TRACE("%s preempt-idle\n", engine->name);
Hmm. I was hoping that we would be able to engineer a single check to
cover all sins. Might have been overly optimistic, but I can dream.
-Chris
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