[PATCH] drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[PATCH] drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[Chris Wilson]

In order to prevent a race condition where we may end up overaccounting
the active state and leaving the busy-stats believing the GPU is 100%
busy, lock out the tasklet while we reconstruct the busy state. There is
no direct spinlock guard for the execlists->port[], so we need to
utilise tasklet_disable() as a synchronous barrier to prevent the only
writer to execlists->port[] from running at the same time as the enable.

Fixes: 4900727d35bb ("drm/i915/pmu: Reconstruct active state on starting busy-stats")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 drivers/gpu/drm/i915/intel_engine_cs.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index d790bdc227ff..b221610f2365 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1943,16 +1943,22 @@ intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, u8 instance)
  */
 int intel_enable_engine_stats(struct intel_engine_cs *engine)
 {
+	struct intel_engine_execlists *execlists = &engine->execlists;
 	unsigned long flags;
+	int err = 0;
 
 	if (!intel_engine_supports_stats(engine))
 		return -ENODEV;
 
+	tasklet_disable(&execlists->tasklet);
 	spin_lock_irqsave(&engine->stats.lock, flags);
-	if (engine->stats.enabled == ~0)
-		goto busy;
+
+	if (unlikely(engine->stats.enabled == ~0)) {
+		err = -EBUSY;
+		goto unlock;
+	}
+
 	if (engine->stats.enabled++ == 0) {
-		struct intel_engine_execlists *execlists = &engine->execlists;
 		const struct execlist_port *port = execlists->port;
 		unsigned int num_ports = execlists_num_ports(execlists);
 
@@ -1967,14 +1973,12 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
 		if (engine->stats.active)
 			engine->stats.start = engine->stats.enabled_at;
 	}
-	spin_unlock_irqrestore(&engine->stats.lock, flags);
 
-	return 0;
-
-busy:
+unlock:
 	spin_unlock_irqrestore(&engine->stats.lock, flags);
+	tasklet_enable(&execlists->tasklet);
 
-	return -EBUSY;
+	return err;
 }
 
 static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)
-- 
2.15.1

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Re: [PATCH] drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[Tvrtko Ursulin]

On 15/01/2018 09:20, Chris Wilson wrote:
> In order to prevent a race condition where we may end up overaccounting
> the active state and leaving the busy-stats believing the GPU is 100%
> busy, lock out the tasklet while we reconstruct the busy state. There is
> no direct spinlock guard for the execlists->port[], so we need to
> utilise tasklet_disable() as a synchronous barrier to prevent the only
> writer to execlists->port[] from running at the same time as the enable.
> 
> Fixes: 4900727d35bb ("drm/i915/pmu: Reconstruct active state on starting busy-stats")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/intel_engine_cs.c | 20 ++++++++++++--------
>   1 file changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index d790bdc227ff..b221610f2365 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -1943,16 +1943,22 @@ intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, u8 instance)
>    */
>   int intel_enable_engine_stats(struct intel_engine_cs *engine)
>   {
> +	struct intel_engine_execlists *execlists = &engine->execlists;
>   	unsigned long flags;
> +	int err = 0;
>   
>   	if (!intel_engine_supports_stats(engine))
>   		return -ENODEV;
>   
> +	tasklet_disable(&execlists->tasklet);
>   	spin_lock_irqsave(&engine->stats.lock, flags);
> -	if (engine->stats.enabled == ~0)
> -		goto busy;
> +
> +	if (unlikely(engine->stats.enabled == ~0)) {
> +		err = -EBUSY;
> +		goto unlock;
> +	}
> +
>   	if (engine->stats.enabled++ == 0) {
> -		struct intel_engine_execlists *execlists = &engine->execlists;
>   		const struct execlist_port *port = execlists->port;
>   		unsigned int num_ports = execlists_num_ports(execlists);
>   
> @@ -1967,14 +1973,12 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
>   		if (engine->stats.active)
>   			engine->stats.start = engine->stats.enabled_at;
>   	}
> -	spin_unlock_irqrestore(&engine->stats.lock, flags);
>   
> -	return 0;
> -
> -busy:
> +unlock:
>   	spin_unlock_irqrestore(&engine->stats.lock, flags);
> +	tasklet_enable(&execlists->tasklet);
>   
> -	return -EBUSY;
> +	return err;
>   }
>   
>   static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)
> 

Hopefully the end of the immediate trouble, with only beautification 
remaining.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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✓ Fi.CI.BAT: success for drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[Patchwork]

== Series Details ==

Series: drm/i915: Lock out execlist tasklet while peeking inside for busy-stats
URL   : https://patchwork.freedesktop.org/series/36473/
State : success

== Summary ==

Series 36473v1 drm/i915: Lock out execlist tasklet while peeking inside for busy-stats
https://patchwork.freedesktop.org/api/1.0/series/36473/revisions/1/mbox/

Test debugfs_test:
        Subgroup read_all_entries:
                incomplete -> PASS       (fi-snb-2520m) fdo#103713 +1
Test gem_mmap_gtt:
        Subgroup basic-small-bo-tiledx:
                fail       -> PASS       (fi-gdg-551) fdo#102575
Test kms_pipe_crc_basic:
        Subgroup suspend-read-crc-pipe-c:
                pass       -> DMESG-WARN (fi-kbl-r) fdo#104172

fdo#103713 https://bugs.freedesktop.org/show_bug.cgi?id=103713
fdo#102575 https://bugs.freedesktop.org/show_bug.cgi?id=102575
fdo#104172 https://bugs.freedesktop.org/show_bug.cgi?id=104172

fi-bdw-5557u     total:288  pass:267  dwarn:0   dfail:0   fail:0   skip:21  time:419s
fi-bdw-gvtdvm    total:288  pass:264  dwarn:0   dfail:0   fail:0   skip:24  time:423s
fi-blb-e6850     total:288  pass:223  dwarn:1   dfail:0   fail:0   skip:64  time:371s
fi-bsw-n3050     total:288  pass:242  dwarn:0   dfail:0   fail:0   skip:46  time:488s
fi-bwr-2160      total:288  pass:183  dwarn:0   dfail:0   fail:0   skip:105 time:280s
fi-bxt-j4205     total:288  pass:259  dwarn:0   dfail:0   fail:0   skip:29  time:488s
fi-byt-j1900     total:288  pass:253  dwarn:0   dfail:0   fail:0   skip:35  time:469s
fi-byt-n2820     total:288  pass:249  dwarn:0   dfail:0   fail:0   skip:39  time:468s
fi-cnl-y2        total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:529s
fi-elk-e7500     total:224  pass:168  dwarn:10  dfail:0   fail:0   skip:45 
fi-gdg-551       total:288  pass:180  dwarn:0   dfail:0   fail:0   skip:108 time:274s
fi-glk-1         total:288  pass:260  dwarn:0   dfail:0   fail:0   skip:28  time:511s
fi-hsw-4770r     total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:399s
fi-ilk-650       total:288  pass:228  dwarn:0   dfail:0   fail:0   skip:60  time:415s
fi-ivb-3520m     total:288  pass:259  dwarn:0   dfail:0   fail:0   skip:29  time:456s
fi-ivb-3770      total:288  pass:255  dwarn:0   dfail:0   fail:0   skip:33  time:423s
fi-kbl-7500u     total:288  pass:263  dwarn:1   dfail:0   fail:0   skip:24  time:469s
fi-kbl-7560u     total:288  pass:269  dwarn:0   dfail:0   fail:0   skip:19  time:504s
fi-kbl-7567u     total:288  pass:268  dwarn:0   dfail:0   fail:0   skip:20  time:457s
fi-kbl-r         total:288  pass:260  dwarn:1   dfail:0   fail:0   skip:27  time:504s
fi-pnv-d510      total:288  pass:222  dwarn:1   dfail:0   fail:0   skip:65  time:579s
fi-skl-6260u     total:288  pass:268  dwarn:0   dfail:0   fail:0   skip:20  time:429s
fi-skl-6600u     total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:516s
fi-skl-6700hq    total:288  pass:262  dwarn:0   dfail:0   fail:0   skip:26  time:529s
fi-skl-6700k2    total:288  pass:264  dwarn:0   dfail:0   fail:0   skip:24  time:495s
fi-skl-6770hq    total:288  pass:268  dwarn:0   dfail:0   fail:0   skip:20  time:492s
fi-snb-2520m     total:245  pass:211  dwarn:0   dfail:0   fail:0   skip:33 
fi-snb-2600      total:288  pass:248  dwarn:0   dfail:0   fail:0   skip:40  time:398s
Blacklisted hosts:
fi-cfl-s2        total:288  pass:262  dwarn:0   dfail:0   fail:0   skip:26  time:568s
fi-glk-dsi       total:288  pass:258  dwarn:0   dfail:0   fail:0   skip:30  time:466s

254125b984264731491e1eafbe58bc50e84a032d drm-tip: 2018y-01m-15d-09h-31m-31s UTC integration manifest
85e0cababafe drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_7667/issues.html
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✓ Fi.CI.IGT: success for drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[Patchwork]

== Series Details ==

Series: drm/i915: Lock out execlist tasklet while peeking inside for busy-stats
URL   : https://patchwork.freedesktop.org/series/36473/
State : success

== Summary ==

Test kms_flip:
        Subgroup plain-flip-fb-recreate:
                fail       -> PASS       (shard-hsw) fdo#100368
        Subgroup vblank-vs-dpms-suspend:
                fail       -> PASS       (shard-snb)
Test kms_setmode:
        Subgroup basic:
                fail       -> PASS       (shard-hsw) fdo#99912
Test kms_pipe_crc_basic:
        Subgroup suspend-read-crc-pipe-a:
                incomplete -> PASS       (shard-snb) fdo#103375
Test gem_tiled_swapping:
        Subgroup non-threaded:
                pass       -> INCOMPLETE (shard-hsw) fdo#104218
Test kms_frontbuffer_tracking:
        Subgroup fbc-1p-offscren-pri-shrfb-draw-render:
                fail       -> PASS       (shard-snb) fdo#101623 +1
Test perf:
        Subgroup oa-formats:
                pass       -> FAIL       (shard-hsw) fdo#104151

fdo#100368 https://bugs.freedesktop.org/show_bug.cgi?id=100368
fdo#99912 https://bugs.freedesktop.org/show_bug.cgi?id=99912
fdo#103375 https://bugs.freedesktop.org/show_bug.cgi?id=103375
fdo#104218 https://bugs.freedesktop.org/show_bug.cgi?id=104218
fdo#101623 https://bugs.freedesktop.org/show_bug.cgi?id=101623
fdo#104151 https://bugs.freedesktop.org/show_bug.cgi?id=104151

shard-hsw        total:2644 pass:1502 dwarn:1   dfail:0   fail:9   skip:1131 time:8886s
shard-snb        total:2713 pass:1311 dwarn:1   dfail:0   fail:10  skip:1391 time:7908s
Blacklisted hosts:
shard-apl        total:2691 pass:1667 dwarn:1   dfail:0   fail:21  skip:1001 time:13180s
shard-kbl        total:2713 pass:1808 dwarn:1   dfail:0   fail:23  skip:881 time:10658s

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_7667/shards.html
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Re: ✓ Fi.CI.IGT: success for drm/i915: Lock out execlist tasklet while peeking inside for busy-stats

[Chris Wilson]

Quoting Patchwork (2018-01-15 12:11:48)
> == Series Details ==
> 
> Series: drm/i915: Lock out execlist tasklet while peeking inside for busy-stats
> URL   : https://patchwork.freedesktop.org/series/36473/
> State : success
> 
> == Logs ==
> 
> For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_7667/shards.html

Looks good, pushed. Thanks for the review, hopefully the baseline
remains green now and you can tidy up with confidence.
-Chris
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