Re: [Intel-gfx] [PATCH v2 01/21] drm/i915/gt: Ignore TLB invalidations on idle engines

[Tvrtko Ursulin]

On 18/07/2022 15:53, Mauro Carvalho Chehab wrote:
On Mon, 18 Jul 2022 14:16:10 +0100
Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com> wrote:

On 14/07/2022 13:06, Mauro Carvalho Chehab wrote:
From: Chris Wilson <chris.p.wil...@intel.com>

Check if the device is powered down prior to any engine activity,
as, on such cases, all the TLBs were already invalidated, so an
explicit TLB invalidation is not needed, thus reducing the
performance regression impact due to it.

This becomes more significant with GuC, as it can only do so when
the connection to the GuC is awake.

Cc: sta...@vger.kernel.org
Fixes: 7938d61591d3 ("drm/i915: Flush TLBs before releasing backing store")

Patch itself looks fine but I don't think we closed on the issue of
stable/fixes on this patch?

No, because TLB cache invalidation takes time and causes time outs, which
in turn affects applications and produce Kernel warnings.

There's even open bugs due to TLB timeouts, like this one:

        [424.370996] i915 0000:00:02.0: [drm] *ERROR* rcs0 TLB invalidation did 
not complete in 4ms!

See:
        https://gitlab.freedesktop.org/drm/intel/-/issues/6424

So, while this is a performance regression, it ends causing a
functional regression.

This test is not even particularly stressful. Fair enough - thanks for 
the information.

Acked-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>

Is skipping of the ggtt only bound flush the fix for this particular test?

Regards,

Tvrtko


The first part of this series (patches 1-7) are meant to reduce the
risk of such timeouts by doing TLB invalidation in batch and only
when really needed (userspace-exposed TLBs for GTs that are powered-on
and non-edged).

As they're fixing such regressions, it makes sense c/c stable and having
a fixes tag.

My position here is that, if the functional issue is only with GuC
invalidations, then the tags shouldn't be there (and the huge CC list).

Regards,

Tvrtko

Signed-off-by: Chris Wilson <chris.p.wil...@intel.com>
Cc: Fei Yang <fei.y...@intel.com>
Cc: Andi Shyti <andi.sh...@linux.intel.com>
Cc: Thomas Hellström <thomas.hellst...@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mche...@kernel.org>
---

To avoid mailbombing on a large number of people, only mailing lists were C/C 
on the cover.
See [PATCH v2 00/21] at: 
https://lore.kernel.org/all/cover.1657800199.git.mche...@kernel.org/

   drivers/gpu/drm/i915/gem/i915_gem_pages.c | 10 ++++++----
   drivers/gpu/drm/i915/gt/intel_gt.c        | 17 ++++++++++-------
   drivers/gpu/drm/i915/gt/intel_gt_pm.h     |  3 +++
   3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c 
b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
index 97c820eee115..6835279943df 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
@@ -6,14 +6,15 @@
   
   #include <drm/drm_cache.h>
   
+#include "gt/intel_gt.h"
+#include "gt/intel_gt_pm.h"
+
   #include "i915_drv.h"
   #include "i915_gem_object.h"
   #include "i915_scatterlist.h"
   #include "i915_gem_lmem.h"
   #include "i915_gem_mman.h"
   
-#include "gt/intel_gt.h"
-
   void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
                                 struct sg_table *pages,
                                 unsigned int sg_page_sizes)
@@ -217,10 +218,11 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object 
*obj)
   
   	if (test_and_clear_bit(I915_BO_WAS_BOUND_BIT, &obj->flags)) {
                struct drm_i915_private *i915 = to_i915(obj->base.dev);
+               struct intel_gt *gt = to_gt(i915);
                intel_wakeref_t wakeref;
   
-		with_intel_runtime_pm_if_active(&i915->runtime_pm, wakeref)
-                       intel_gt_invalidate_tlbs(to_gt(i915));
+               with_intel_gt_pm_if_awake(gt, wakeref)
+                       intel_gt_invalidate_tlbs(gt);
        }
   
   	return pages;
diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c 
b/drivers/gpu/drm/i915/gt/intel_gt.c
index 68c2b0d8f187..c4d43da84d8e 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -12,6 +12,7 @@
   
   #include "i915_drv.h"
   #include "intel_context.h"
+#include "intel_engine_pm.h"
   #include "intel_engine_regs.h"
   #include "intel_ggtt_gmch.h"
   #include "intel_gt.h"
@@ -924,6 +925,7 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
        struct drm_i915_private *i915 = gt->i915;
        struct intel_uncore *uncore = gt->uncore;
        struct intel_engine_cs *engine;
+       intel_engine_mask_t awake, tmp;
        enum intel_engine_id id;
        const i915_reg_t *regs;
        unsigned int num = 0;
@@ -947,26 +949,31 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
   
   	GEM_TRACE("\n");
   
-	assert_rpm_wakelock_held(&i915->runtime_pm);
-
        mutex_lock(&gt->tlb_invalidate_lock);
        intel_uncore_forcewake_get(uncore, FORCEWAKE_ALL);
   
   	spin_lock_irq(&uncore->lock); /* serialise invalidate with GT reset */
   
+	awake = 0;
        for_each_engine(engine, gt, id) {
                struct reg_and_bit rb;
   
+		if (!intel_engine_pm_is_awake(engine))
+                       continue;
+
                rb = get_reg_and_bit(engine, regs == gen8_regs, regs, num);
                if (!i915_mmio_reg_offset(rb.reg))
                        continue;
   
   		intel_uncore_write_fw(uncore, rb.reg, rb.bit);
+               awake |= engine->mask;
        }
   
   	spin_unlock_irq(&uncore->lock);
   
-	for_each_engine(engine, gt, id) {
+       for_each_engine_masked(engine, gt, awake, tmp) {
+               struct reg_and_bit rb;
+
                /*
                 * HW architecture suggest typical invalidation time at 40us,
                 * with pessimistic cases up to 100us and a recommendation to
@@ -974,12 +981,8 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
                 */
                const unsigned int timeout_us = 100;
                const unsigned int timeout_ms = 4;
-               struct reg_and_bit rb;
   
   		rb = get_reg_and_bit(engine, regs == gen8_regs, regs, num);
-               if (!i915_mmio_reg_offset(rb.reg))
-                       continue;
-
                if (__intel_wait_for_register_fw(uncore,
                                                 rb.reg, rb.bit, 0,
                                                 timeout_us, timeout_ms,
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h 
b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
index bc898df7a48c..a334787a4939 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
+++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
@@ -55,6 +55,9 @@ static inline void intel_gt_pm_might_put(struct intel_gt *gt)
        for (tmp = 1, intel_gt_pm_get(gt); tmp; \
             intel_gt_pm_put(gt), tmp = 0)
   
+#define with_intel_gt_pm_if_awake(gt, wf) \
+       for (wf = intel_gt_pm_get_if_awake(gt); wf; intel_gt_pm_put_async(gt), 
wf = 0)
+
   static inline int intel_gt_pm_wait_for_idle(struct intel_gt *gt)
   {
        return intel_wakeref_wait_for_idle(&gt->wakeref);