[PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

It seems that the DMC likes to transition between the DC states
a lot when there are no connected displays (no active power
domains) during simple command submission.

This frantic activity on DC states has a terrible impact on the
performance of the overall chip with huge latencies observed in
the interrupt handlers and elsewhere. Simple tests like
igt/gem_latency -n 0 are slowed down by a factor of eight.

Work around it by grabbing a modeset display power domain whilst
there is any GT activity. This seems to be effective in making
the DMC keep its paws off the chip.

On the other hand this may have a negative impact on the overall
power budget of the chip and so could still affect performance.

This version limits the workaround got SKL GT3 and GT4 parts but
this is just due the absence of testing on other platforms. It
is possible we will have to apply it wider.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572
Testcase: igt/gem_exec_nop/headless
Cc: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         | 5 +++++
 drivers/gpu/drm/i915/i915_gem.c         | 4 ++++
 drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
 3 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 320c16df1c9c..4d58e2e28c2f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2990,6 +2990,11 @@ intel_info(const struct drm_i915_private *dev_priv)
 
 #define HAS_DECOUPLED_MMIO(dev_priv) (INTEL_INFO(dev_priv)->has_decoupled_mmio)
 
+#define NEEDS_CSR_GT_PERF_WA(dev_priv) \
+	HAS_CSR(dev_priv) && \
+	(IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv)) && \
+	(dev_priv)->csr.dmc_payload
+
 #include "i915_trace.h"
 
 static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b2727905ef2b..c52d863f409c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3200,7 +3200,11 @@ i915_gem_idle_work_handler(struct work_struct *work)
 
 	if (INTEL_GEN(dev_priv) >= 6)
 		gen6_rps_idle(dev_priv);
+
 	intel_runtime_pm_put(dev_priv);
+
+	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
+		intel_display_power_put(dev_priv, POWER_DOMAIN_MODESET);
 out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 10361c7e3b37..10a3b51f6362 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -873,6 +873,9 @@ static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
 
 	GEM_BUG_ON(!dev_priv->gt.active_requests);
 
+	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
+		intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
+
 	intel_runtime_pm_get_noresume(dev_priv);
 	dev_priv->gt.awake = true;
 
-- 
2.9.3

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Re: [PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Chris Wilson]

On Fri, May 05, 2017 at 12:43:21PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> It seems that the DMC likes to transition between the DC states
> a lot when there are no connected displays (no active power
> domains) during simple command submission.
> 
> This frantic activity on DC states has a terrible impact on the
> performance of the overall chip with huge latencies observed in
> the interrupt handlers and elsewhere. Simple tests like
> igt/gem_latency -n 0 are slowed down by a factor of eight.
> 
> Work around it by grabbing a modeset display power domain whilst
> there is any GT activity. This seems to be effective in making
> the DMC keep its paws off the chip.
> 
> On the other hand this may have a negative impact on the overall
> power budget of the chip and so could still affect performance.

Please add this as a comment to the code, I think in mark_busy(). I
don't think this w/a will remain applicable forever and so merits a
continual reminder and being discussed again in future.
 
> This version limits the workaround got SKL GT3 and GT4 parts but
> this is just due the absence of testing on other platforms. It
> is possible we will have to apply it wider.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572
> Testcase: igt/gem_exec_nop/headless
> Cc: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h         | 5 +++++
>  drivers/gpu/drm/i915/i915_gem.c         | 4 ++++
>  drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
>  3 files changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 320c16df1c9c..4d58e2e28c2f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2990,6 +2990,11 @@ intel_info(const struct drm_i915_private *dev_priv)
>  
>  #define HAS_DECOUPLED_MMIO(dev_priv) (INTEL_INFO(dev_priv)->has_decoupled_mmio)
>  
> +#define NEEDS_CSR_GT_PERF_WA(dev_priv) \
> +	HAS_CSR(dev_priv) && \
> +	(IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv)) && \
> +	(dev_priv)->csr.dmc_payload

csr.dmc_payload is a bit of a surprise, but looks correct.

Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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✓ Fi.CI.BAT: success for drm/i915: Restore GT performance in headless mode with DMC loaded

[Patchwork]

== Series Details ==

Series: drm/i915: Restore GT performance in headless mode with DMC loaded
URL   : https://patchwork.freedesktop.org/series/24017/
State : success

== Summary ==

Series 24017v1 drm/i915: Restore GT performance in headless mode with DMC loaded
https://patchwork.freedesktop.org/api/1.0/series/24017/revisions/1/mbox/

fi-bdw-5557u     total:278  pass:267  dwarn:0   dfail:0   fail:0   skip:11  time:429s
fi-bdw-gvtdvm    total:278  pass:256  dwarn:8   dfail:0   fail:0   skip:14  time:433s
fi-bsw-n3050     total:278  pass:242  dwarn:0   dfail:0   fail:0   skip:36  time:577s
fi-bxt-j4205     total:278  pass:259  dwarn:0   dfail:0   fail:0   skip:19  time:509s
fi-bxt-t5700     total:278  pass:258  dwarn:0   dfail:0   fail:0   skip:20  time:548s
fi-byt-j1900     total:278  pass:254  dwarn:0   dfail:0   fail:0   skip:24  time:490s
fi-byt-n2820     total:278  pass:250  dwarn:0   dfail:0   fail:0   skip:28  time:485s
fi-hsw-4770      total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time:409s
fi-hsw-4770r     total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time:408s
fi-ilk-650       total:278  pass:228  dwarn:0   dfail:0   fail:0   skip:50  time:416s
fi-ivb-3520m     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:495s
fi-ivb-3770      total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:471s
fi-kbl-7500u     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:458s
fi-kbl-7560u     total:278  pass:267  dwarn:1   dfail:0   fail:0   skip:10  time:566s
fi-skl-6260u     total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time:458s
fi-skl-6700hq    total:278  pass:261  dwarn:0   dfail:0   fail:0   skip:17  time:569s
fi-skl-6700k     total:278  pass:256  dwarn:4   dfail:0   fail:0   skip:18  time:460s
fi-skl-6770hq    total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time:489s
fi-skl-gvtdvm    total:278  pass:265  dwarn:0   dfail:0   fail:0   skip:13  time:431s
fi-snb-2520m     total:278  pass:250  dwarn:0   dfail:0   fail:0   skip:28  time:531s
fi-snb-2600      total:278  pass:249  dwarn:0   dfail:0   fail:0   skip:29  time:408s

369880c1680bf9bde467a40d2a03d3ad32341281 drm-tip: 2017y-05m-04d-15h-00m-33s UTC integration manifest
e0b135e drm/i915: Restore GT performance in headless mode with DMC loaded

== Logs ==

For more details see: https://intel-gfx-ci.01.org/CI/Patchwork_4630/
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Re: [PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Ville Syrjälä]

On Fri, May 05, 2017 at 12:43:21PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> It seems that the DMC likes to transition between the DC states
> a lot when there are no connected displays (no active power
> domains) during simple command submission.

Is it trapping on some interrupt register accesses or what? And
if so which registers are affected?

> 
> This frantic activity on DC states has a terrible impact on the
> performance of the overall chip with huge latencies observed in
> the interrupt handlers and elsewhere. Simple tests like
> igt/gem_latency -n 0 are slowed down by a factor of eight.
> 
> Work around it by grabbing a modeset display power domain whilst
> there is any GT activity. This seems to be effective in making
> the DMC keep its paws off the chip.
> 
> On the other hand this may have a negative impact on the overall
> power budget of the chip and so could still affect performance.
> 
> This version limits the workaround got SKL GT3 and GT4 parts but
> this is just due the absence of testing on other platforms. It
> is possible we will have to apply it wider.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572
> Testcase: igt/gem_exec_nop/headless
> Cc: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h         | 5 +++++
>  drivers/gpu/drm/i915/i915_gem.c         | 4 ++++
>  drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
>  3 files changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 320c16df1c9c..4d58e2e28c2f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2990,6 +2990,11 @@ intel_info(const struct drm_i915_private *dev_priv)
>  
>  #define HAS_DECOUPLED_MMIO(dev_priv) (INTEL_INFO(dev_priv)->has_decoupled_mmio)
>  
> +#define NEEDS_CSR_GT_PERF_WA(dev_priv) \
> +	HAS_CSR(dev_priv) && \
> +	(IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv)) && \
> +	(dev_priv)->csr.dmc_payload
> +
>  #include "i915_trace.h"
>  
>  static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index b2727905ef2b..c52d863f409c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3200,7 +3200,11 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  
>  	if (INTEL_GEN(dev_priv) >= 6)
>  		gen6_rps_idle(dev_priv);
> +
>  	intel_runtime_pm_put(dev_priv);
> +
> +	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
> +		intel_display_power_put(dev_priv, POWER_DOMAIN_MODESET);
>  out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 10361c7e3b37..10a3b51f6362 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -873,6 +873,9 @@ static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
>  
>  	GEM_BUG_ON(!dev_priv->gt.active_requests);
>  
> +	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
> +		intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
> +
>  	intel_runtime_pm_get_noresume(dev_priv);
>  	dev_priv->gt.awake = true;
>  
> -- 
> 2.9.3
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
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Intel OTC
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Re: [PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Tvrtko Ursulin]

On 05/05/2017 15:49, Ville Syrjälä wrote:
> On Fri, May 05, 2017 at 12:43:21PM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> It seems that the DMC likes to transition between the DC states
>> a lot when there are no connected displays (no active power
>> domains) during simple command submission.
>
> Is it trapping on some interrupt register accesses or what? And
> if so which registers are affected?

It looks like GT IIR or something along those lines it but I couldn't 
say with total confidence. It is just a guess. Firmware binary 
definitely "mentions" those registers as can be seen by inspecting it 
with a hex editor.

The data I collected at least seems to present a correlation between the 
batch frequency and DC state transition frequency:

tgt	DC		irqs	irqs/s	irq	batch/s	DC/s	DC/batch
submit	transitions			/
freq					batch
========================================================================
10000	20000		78300	7830.00	1.96	4000.00	2000.00	0.50
9901	14000		52855	7550.71	1.32	5714.29	2000.00	0.35
9524	13500		49100	7328.36	1.23	5970.15	2014.93	0.34
9091	13500		49200	7235.29	1.23	5882.35	1985.29	0.34
5000	16900		33290	3916.47	0.83	4705.88	1988.24	0.42
3333	27800		69550	4932.62	1.74	2836.88	1971.63	0.70
1667	57200		80200	2655.63	2.01	1324.50	1894.04	1.43
909	80000		80034	1482.11	2.00	740.74	1481.48	2.00
476	87000		80039	820.91	2.00	410.26	892.31	2.18
196	160000		80055	334.40	2.00	167.08	668.34	4.00

Submitted batches were ~100us long in all cases. So with low batch 
frequency it looks pretty believable. For example when we have 167.08 
batches/s, we have 334.40 irq/s - which is double - as expected for 
execlists. And we get again double that in terms of DC transitions per 
second. Each irq is one GT IIR write from the GPU side, and another from 
the CPU side.

This was actually Imre's suggestion btw. Before I was only looking at 
the irq/s to DC/s correlation which was confusing me a lot since there 
are more of the latter, so I thought it can't be the trigger. But once 
Imre mentioned the possibility that things are triggered by IIR register 
writes numbers started making more sense.

Then with higher batch frequencies the ratio starts falling, is it 
because DC transitions are too slow to keep up, or something else I am 
not sure.

Regards,

Tvrtko
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Re: [PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Ville Syrjälä]

On Fri, May 05, 2017 at 05:13:58PM +0100, Tvrtko Ursulin wrote:
> 
> On 05/05/2017 15:49, Ville Syrjälä wrote:
> > On Fri, May 05, 2017 at 12:43:21PM +0100, Tvrtko Ursulin wrote:
> >> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >> It seems that the DMC likes to transition between the DC states
> >> a lot when there are no connected displays (no active power
> >> domains) during simple command submission.
> >
> > Is it trapping on some interrupt register accesses or what? And
> > if so which registers are affected?
> 
> It looks like GT IIR or something along those lines it but I couldn't 
> say with total confidence.

<read DC counters>
for i in `seq 1 100` ; do IGT_NO_FORCEWAKE=1 intel_reg read <whatever> ; done
<read DC counters>

Should be a pretty trivial to run that against the suspect
registers.

> It is just a guess. Firmware binary 
> definitely "mentions" those registers as can be seen by inspecting it 
> with a hex editor.
> 
> The data I collected at least seems to present a correlation between the 
> batch frequency and DC state transition frequency:
> 
> tgt	DC		irqs	irqs/s	irq	batch/s	DC/s	DC/batch
> submit	transitions			/
> freq					batch
> ========================================================================
> 10000	20000		78300	7830.00	1.96	4000.00	2000.00	0.50
> 9901	14000		52855	7550.71	1.32	5714.29	2000.00	0.35
> 9524	13500		49100	7328.36	1.23	5970.15	2014.93	0.34
> 9091	13500		49200	7235.29	1.23	5882.35	1985.29	0.34
> 5000	16900		33290	3916.47	0.83	4705.88	1988.24	0.42
> 3333	27800		69550	4932.62	1.74	2836.88	1971.63	0.70
> 1667	57200		80200	2655.63	2.01	1324.50	1894.04	1.43
> 909	80000		80034	1482.11	2.00	740.74	1481.48	2.00
> 476	87000		80039	820.91	2.00	410.26	892.31	2.18
> 196	160000		80055	334.40	2.00	167.08	668.34	4.00
> 
> Submitted batches were ~100us long in all cases. So with low batch 
> frequency it looks pretty believable. For example when we have 167.08 
> batches/s, we have 334.40 irq/s - which is double - as expected for 
> execlists. And we get again double that in terms of DC transitions per 
> second. Each irq is one GT IIR write from the GPU side, and another from 
> the CPU side.

GPU doesn't actually write the IIRs. It's just latching stuff from the
ISR. Whether the ISR edge or some higher level interrupt event actually
causes the DMC to kick into action isn't clear at all. My original
impressions was that it just traps the register accesses.

-- 
Ville Syrjälä
Intel OTC
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Re: [PATCH] drm/i915: Restore GT performance in headless mode with DMC loaded

[Jani Nikula]

On Fri, 05 May 2017, Tvrtko Ursulin <tursulin@ursulin.net> wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> It seems that the DMC likes to transition between the DC states
> a lot when there are no connected displays (no active power
> domains) during simple command submission.
>
> This frantic activity on DC states has a terrible impact on the
> performance of the overall chip with huge latencies observed in
> the interrupt handlers and elsewhere. Simple tests like
> igt/gem_latency -n 0 are slowed down by a factor of eight.
>
> Work around it by grabbing a modeset display power domain whilst
> there is any GT activity. This seems to be effective in making
> the DMC keep its paws off the chip.
>
> On the other hand this may have a negative impact on the overall
> power budget of the chip and so could still affect performance.
>
> This version limits the workaround got SKL GT3 and GT4 parts but
> this is just due the absence of testing on other platforms. It
> is possible we will have to apply it wider.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572
> Testcase: igt/gem_exec_nop/headless
> Cc: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h         | 5 +++++
>  drivers/gpu/drm/i915/i915_gem.c         | 4 ++++
>  drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
>  3 files changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 320c16df1c9c..4d58e2e28c2f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2990,6 +2990,11 @@ intel_info(const struct drm_i915_private *dev_priv)
>  
>  #define HAS_DECOUPLED_MMIO(dev_priv) (INTEL_INFO(dev_priv)->has_decoupled_mmio)
>  
> +#define NEEDS_CSR_GT_PERF_WA(dev_priv) \
> +	HAS_CSR(dev_priv) && \
> +	(IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv)) && \
> +	(dev_priv)->csr.dmc_payload

Nitpick, the whole thing could use braces around it for consistency,
although I don't see any sane use of the macro causing precedence
surprises.

BR,
Jani.

> +
>  #include "i915_trace.h"
>  
>  static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index b2727905ef2b..c52d863f409c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3200,7 +3200,11 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  
>  	if (INTEL_GEN(dev_priv) >= 6)
>  		gen6_rps_idle(dev_priv);
> +
>  	intel_runtime_pm_put(dev_priv);
> +
> +	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
> +		intel_display_power_put(dev_priv, POWER_DOMAIN_MODESET);
>  out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 10361c7e3b37..10a3b51f6362 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -873,6 +873,9 @@ static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
>  
>  	GEM_BUG_ON(!dev_priv->gt.active_requests);
>  
> +	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
> +		intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
> +
>  	intel_runtime_pm_get_noresume(dev_priv);
>  	dev_priv->gt.awake = true;

-- 
Jani Nikula, Intel Open Source Technology Center
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[PATCH v2] drm/i915: Restore GT performance in headless mode with DMC loaded

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

It seems that the DMC likes to transition between the DC states
a lot when there are no connected displays (no active power
domains) during simple command submission.

This frantic activity on DC states has a terrible impact on the
performance of the overall chip with huge latencies observed in
the interrupt handlers and elsewhere. Simple tests like
igt/gem_latency -n 0 are slowed down by a factor of eight.

Work around it by grabbing a modeset display power domain whilst
there is any GT activity. This seems to be effective in making
the DMC keep its paws off the chip.

On the other hand this may have a negative impact on the overall
power budget of the chip and so could still affect performance.

This version limits the workaround got SKL GT3 and GT4 parts but
this is just due the absence of testing on other platforms. It
is possible we will have to apply it wider.

v2:
 * Add commit text as comment in i915_gem_mark_busy. (Chris Wilson)
 * Protect macro body with braces. (Jani Nikula)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572
Testcase: igt/gem_exec_nop/headless
Cc: Imre Deak <imre.deak@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h         |  5 +++++
 drivers/gpu/drm/i915/i915_gem.c         |  4 ++++
 drivers/gpu/drm/i915/i915_gem_request.c | 17 +++++++++++++++++
 3 files changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 320c16df1c9c..509b398d054d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2990,6 +2990,11 @@ intel_info(const struct drm_i915_private *dev_priv)
 
 #define HAS_DECOUPLED_MMIO(dev_priv) (INTEL_INFO(dev_priv)->has_decoupled_mmio)
 
+#define NEEDS_CSR_GT_PERF_WA(dev_priv) \
+	(HAS_CSR(dev_priv) && \
+	(IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv)) && \
+	(dev_priv)->csr.dmc_payload)
+
 #include "i915_trace.h"
 
 static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b2727905ef2b..c52d863f409c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3200,7 +3200,11 @@ i915_gem_idle_work_handler(struct work_struct *work)
 
 	if (INTEL_GEN(dev_priv) >= 6)
 		gen6_rps_idle(dev_priv);
+
 	intel_runtime_pm_put(dev_priv);
+
+	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
+		intel_display_power_put(dev_priv, POWER_DOMAIN_MODESET);
 out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 10361c7e3b37..c47c983b874e 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -873,6 +873,23 @@ static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
 
 	GEM_BUG_ON(!dev_priv->gt.active_requests);
 
+	/*
+	 * It seems that the DMC likes to transition between the DC states
+	 * a lot when there are no connected displays (no active power
+	 * domains) during simple command submission.
+	 *
+	 * This frantic activity on DC states has a terrible impact on the
+	 * performance of the overall chip with huge latencies observed in
+	 * the interrupt handlers and elsewhere. Simple tests like
+	 * igt/gem_latency -n 0 are slowed down by a factor of eight.
+	 *
+	 * Work around it by grabbing a modeset display power domain whilst
+	 * there is any GT activity. This seems to be effective in making
+	 * the DMC keep its paws off the chip.
+	 */
+	if (NEEDS_CSR_GT_PERF_WA(dev_priv))
+		intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
+
 	intel_runtime_pm_get_noresume(dev_priv);
 	dev_priv->gt.awake = true;
 
-- 
2.9.3

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✓ Fi.CI.BAT: success for drm/i915: Restore GT performance in headless mode with DMC loaded (rev2)

[Patchwork]

== Series Details ==

Series: drm/i915: Restore GT performance in headless mode with DMC loaded (rev2)
URL   : https://patchwork.freedesktop.org/series/24017/
State : success

== Summary ==

Series 24017v2 drm/i915: Restore GT performance in headless mode with DMC loaded
https://patchwork.freedesktop.org/api/1.0/series/24017/revisions/2/mbox/

fi-bdw-5557u     total:278  pass:267  dwarn:0   dfail:0   fail:0   skip:11  time:432s
fi-bdw-gvtdvm    total:278  pass:256  dwarn:8   dfail:0   fail:0   skip:14  time:424s
fi-bsw-n3050     total:278  pass:242  dwarn:0   dfail:0   fail:0   skip:36  time:586s
fi-bxt-j4205     total:278  pass:259  dwarn:0   dfail:0   fail:0   skip:19  time:506s
fi-bxt-t5700     total:278  pass:258  dwarn:0   dfail:0   fail:0   skip:20  time:564s
fi-byt-j1900     total:278  pass:254  dwarn:0   dfail:0   fail:0   skip:24  time:487s
fi-byt-n2820     total:278  pass:250  dwarn:0   dfail:0   fail:0   skip:28  time:479s
fi-hsw-4770      total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time:416s
fi-hsw-4770r     total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time:406s
fi-ilk-650       total:278  pass:228  dwarn:0   dfail:0   fail:0   skip:50  time:416s
fi-ivb-3520m     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:498s
fi-ivb-3770      total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:466s
fi-kbl-7500u     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time:456s
fi-kbl-7560u     total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time:571s
fi-skl-6260u     total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time:451s
fi-skl-6700hq    total:278  pass:261  dwarn:0   dfail:0   fail:0   skip:17  time:565s
fi-skl-6700k     total:278  pass:256  dwarn:4   dfail:0   fail:0   skip:18  time:455s
fi-skl-6770hq    total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time:492s
fi-snb-2520m     total:278  pass:250  dwarn:0   dfail:0   fail:0   skip:28  time:528s
fi-snb-2600      total:278  pass:249  dwarn:0   dfail:0   fail:0   skip:29  time:409s
fi-skl-gvtdvm failed to collect. IGT log at Patchwork_4639/fi-skl-gvtdvm/igt.log

f3c6147e2a7879ee7face0b7b634dd26704fc3d4 drm-tip: 2017y-05m-08d-11h-23m-22s UTC integration manifest
6a61edd drm/i915: Restore GT performance in headless mode with DMC loaded

== Logs ==

For more details see: https://intel-gfx-ci.01.org/CI/Patchwork_4639/
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