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Date:   Thu, 28 Jul 2022 14:34:30 +0200
From:   Mauro Carvalho Chehab <mauro.chehab@linux.intel.com>
To:     Andi Shyti <andi.shyti@linux.intel.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        David Airlie <airlied@linux.ie>,
        intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org,
        Christian =?UTF-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        linaro-mm-sig@lists.linaro.org,
        Sumit Semwal <sumit.semwal@linaro.org>,
        linux-media@vger.kernel.org
Subject: Re: [Intel-gfx] [PATCH v3 0/6] drm/i915: reduce TLB performance
 regressions
Message-ID: <20220728143430.0d0d875a@maurocar-mobl2>
In-Reply-To: <YuJ8K7W50VeHNAGX@alfio.lan>
References: <cover.1658924372.git.mchehab@kernel.org>
        <YuJ8K7W50VeHNAGX@alfio.lan>
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Hi Andi,

On Thu, 28 Jul 2022 14:08:11 +0200
Andi Shyti <andi.shyti@linux.intel.com> wrote:

> Hi Mauro,
> 
> Pushed in drm-intel-gt-next.

Thank you!

I submitted two additional patches moving the TLB code into its own file,
and adding the documentation for it, as agreed during patch 5/6 review:

	https://patchwork.freedesktop.org/series/106806/

That should make easier to maintain TLB-related code and have such
functions properly documented.

Regards,
Mauro


> 
> Thanks,
> Andi
> 
> On Wed, Jul 27, 2022 at 02:29:50PM +0200, Mauro Carvalho Chehab wrote:
> > Doing TLB invalidation cause performance regressions, like:
> > 	[424.370996] i915 0000:00:02.0: [drm] *ERROR* rcs0 TLB invalidation did not complete in 4ms!
> > 
> > As reported at:
> > 	https://gitlab.freedesktop.org/drm/intel/-/issues/6424
> > 
> > as this is an expensive operation. So, reduce the need of it by:
> >   - checking if the engine is awake;
> >   - checking if the engine is not wedged;
> >   - batching operations.
> > 
> > Additionally, add a workaround for a known hardware issue on some GPUs.
> > 
> > In order to double-check that this series won't be introducing any regressions,
> > I used this new IGT test:
> > 
> > https://patchwork.freedesktop.org/patch/495684/?series=106757&rev=1
> > 
> > Checking the results for 3 different patchsets, on Broadwell:
> > 
> > 1) On the top of drm-tip (2022y-07m-14d-08h-35m-36) - e. g. with TLB
> > invalidation and serialization patches:
> > 
> > 	$ sudo build/tests/gem_exec_tlb|grep Subtest
> > 	Subtest close-clear: SUCCESS (10.490s)
> > 	Subtest madv-clear: SUCCESS (10.484s)
> > 	Subtest u-unmap-clear: SUCCESS (10.527s)
> > 	Subtest u-shrink-clear: SUCCESS (10.506s)
> > 	Subtest close-dumb: SUCCESS (10.165s)
> > 	Subtest madv-dumb: SUCCESS (10.177s)
> > 	Subtest u-unmap-dumb: SUCCESS (10.172s)
> > 	Subtest u-shrink-dumb: SUCCESS (10.172s)
> > 
> > 2) With the new version of the batch TLB invalidation patches from this series:
> > 
> > 	$ sudo build/tests/gem_exec_tlb|grep Subtest
> > 	Subtest close-clear: SUCCESS (10.483s)
> > 	Subtest madv-clear: SUCCESS (10.495s)
> > 	Subtest u-unmap-clear: SUCCESS (10.545s)
> > 	Subtest u-shrink-clear: SUCCESS (10.508s)
> > 	Subtest close-dumb: SUCCESS (10.172s)
> > 	Subtest madv-dumb: SUCCESS (10.169s)
> > 	Subtest u-unmap-dumb: SUCCESS (10.174s)
> > 	Subtest u-shrink-dumb: SUCCESS (10.176s)
> > 
> > 3) Changing the TLB invalidation routine to do nothing[1]:
> > 
> > 	$ sudo ~/freedesktop-igt/build/tests/gem_exec_tlb|grep Subtest
> > 	(gem_exec_tlb:1958) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1958) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1958) CRITICAL: Found deadbeef in a new (clear) buffer after 3 tries!
> > 	(gem_exec_tlb:1956) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1956) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1956) CRITICAL: Found deadbeef in a new (clear) buffer after 89 tries!
> > 	(gem_exec_tlb:1957) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1957) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1957) CRITICAL: Found deadbeef in a new (clear) buffer after 256 tries!
> > 	(gem_exec_tlb:1960) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1960) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1960) CRITICAL: Found deadbeef in a new (clear) buffer after 845 tries!
> > 	(gem_exec_tlb:1961) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1961) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1961) CRITICAL: Found deadbeef in a new (clear) buffer after 1138 tries!
> > 	(gem_exec_tlb:1954) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1954) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1954) CRITICAL: Found deadbeef in a new (clear) buffer after 1359 tries!
> > 	(gem_exec_tlb:1955) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1955) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1955) CRITICAL: Found deadbeef in a new (clear) buffer after 1794 tries!
> > 	(gem_exec_tlb:1959) CRITICAL: Test assertion failure function check_bo, file ../tests/i915/gem_exec_tlb.c:384:
> > 	(gem_exec_tlb:1959) CRITICAL: Failed assertion: !sq
> > 	(gem_exec_tlb:1959) CRITICAL: Found deadbeef in a new (clear) buffer after 2139 tries!
> > 	Dynamic subtest smem0 failed.
> > 	**** DEBUG ****
> > 	(gem_exec_tlb:1944) DEBUG: 2M hole:200000 contains poison:6b6b6b6b
> > 	(gem_exec_tlb:1944) DEBUG: Running writer for 200000 at 300000 on bcs0
> > 	(gem_exec_tlb:1944) DEBUG: Closing hole:200000 on rcs0, sample:deadbeef
> > 	(gem_exec_tlb:1944) DEBUG: Rechecking hole:200000, sample:6b6b6b6b
> > 	****  END  ****
> > 	Subtest close-clear: FAIL (10.434s)
> > 	Subtest madv-clear: SUCCESS (10.479s)
> > 	Subtest u-unmap-clear: SUCCESS (10.512s)
> > 
> > In summary, the test does properly detect fail when TLB cache invalidation doesn't happen,
> > as shown at result (3). It also shows that both current drm-tip and drm-tip with this series
> > applied don't have TLB invalidation cache issues.
> > 
> > [1] I applied this patch on the top of drm-tip:
> > 
> > 	diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
> > 	index 68c2b0d8f187..0aefcd7be5e9 100644
> > 	--- a/drivers/gpu/drm/i915/gt/intel_gt.c
> > 	+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
> > 	@@ -930,0 +931,3 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
> > 	+	// HACK: don't do TLB invalidations!!!
> > 	+	return;
> > 	+
> > 
> > Regards,
> > Mauro
> > 
> > Chris Wilson (4):
> >   drm/i915/gt: Ignore TLB invalidations on idle engines
> >   drm/i915/gt: Invalidate TLB of the OA unit at TLB invalidations
> >   drm/i915/gt: Skip TLB invalidations once wedged
> >   drm/i915/gt: Batch TLB invalidations
> > 
> > Mauro Carvalho Chehab (2):
> >   drm/i915/gt: document with_intel_gt_pm_if_awake()
> >   drm/i915/gt: describe the new tlb parameter at i915_vma_resource
> > 
> >  .../gpu/drm/i915/gem/i915_gem_object_types.h  |  3 +-
> >  drivers/gpu/drm/i915/gem/i915_gem_pages.c     | 25 +++---
> >  drivers/gpu/drm/i915/gt/intel_gt.c            | 77 +++++++++++++++----
> >  drivers/gpu/drm/i915/gt/intel_gt.h            | 12 ++-
> >  drivers/gpu/drm/i915/gt/intel_gt_pm.h         | 11 +++
> >  drivers/gpu/drm/i915/gt/intel_gt_types.h      | 18 ++++-
> >  drivers/gpu/drm/i915/gt/intel_ppgtt.c         |  8 +-
> >  drivers/gpu/drm/i915/i915_vma.c               | 33 ++++++--
> >  drivers/gpu/drm/i915/i915_vma.h               |  1 +
> >  drivers/gpu/drm/i915/i915_vma_resource.c      |  9 ++-
> >  drivers/gpu/drm/i915/i915_vma_resource.h      |  6 +-
> >  11 files changed, 163 insertions(+), 40 deletions(-)
> > 
> > -- 
> > 2.36.1
> >