99 lines
4.2 KiB
Diff
99 lines
4.2 KiB
Diff
From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
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Date: Wed, 5 Jul 2023 10:30:25 +0100
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Subject: [PATCH] drm/i915: Do not disable preemption for resets
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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Commit ade8a0f59844 ("drm/i915: Make all GPU resets atomic") added a
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preempt disable section over the hardware reset callback to prepare the
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driver for being able to reset from atomic contexts.
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In retrospect I can see that the work item at a time was about removing
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the struct mutex from the reset path. Code base also briefly entertained
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the idea of doing the reset under stop_machine in order to serialize
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userspace mmap and temporary glitch in the fence registers (see
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eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex"),
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but that never materialized and was soon removed in 2caffbf11762
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("drm/i915: Revoke mmaps and prevent access to fence registers across
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reset") and replaced with a SRCU based solution.
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As such, as far as I can see, today we still have a requirement that
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resets must not sleep (invoked from submission tasklets), but no need to
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support invoking them from a truly atomic context.
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Given that the preemption section is problematic on RT kernels, since the
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uncore lock becomes a sleeping lock and so is invalid in such section,
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lets try and remove it. Potential downside is that our short waits on GPU
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to complete the reset may get extended if CPU scheduling interferes, but
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in practice that probably isn't a deal breaker.
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In terms of mechanics, since the preemption disabled block is being
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removed we just need to replace a few of the wait_for_atomic macros into
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busy looping versions which will work (and not complain) when called from
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non-atomic sections.
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Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
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Cc: Chris Wilson <chris.p.wilson@intel.com>
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Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
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Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Link: https://lore.kernel.org/r/20230705093025.3689748-1-tvrtko.ursulin@linux.intel.com
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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drivers/gpu/drm/i915/gt/intel_reset.c | 12 +++++-------
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1 file changed, 5 insertions(+), 7 deletions(-)
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--- a/drivers/gpu/drm/i915/gt/intel_reset.c
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+++ b/drivers/gpu/drm/i915/gt/intel_reset.c
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@@ -164,13 +164,13 @@ static int i915_do_reset(struct intel_gt
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/* Assert reset for at least 20 usec, and wait for acknowledgement. */
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pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
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udelay(50);
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- err = wait_for_atomic(i915_in_reset(pdev), 50);
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+ err = _wait_for_atomic(i915_in_reset(pdev), 50, 0);
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/* Clear the reset request. */
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pci_write_config_byte(pdev, I915_GDRST, 0);
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udelay(50);
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if (!err)
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- err = wait_for_atomic(!i915_in_reset(pdev), 50);
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+ err = _wait_for_atomic(!i915_in_reset(pdev), 50, 0);
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return err;
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}
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@@ -190,7 +190,7 @@ static int g33_do_reset(struct intel_gt
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struct pci_dev *pdev = to_pci_dev(gt->i915->drm.dev);
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pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
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- return wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ return _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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}
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static int g4x_do_reset(struct intel_gt *gt,
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@@ -207,7 +207,7 @@ static int g4x_do_reset(struct intel_gt
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pci_write_config_byte(pdev, I915_GDRST,
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GRDOM_MEDIA | GRDOM_RESET_ENABLE);
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- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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if (ret) {
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GT_TRACE(gt, "Wait for media reset failed\n");
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goto out;
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@@ -215,7 +215,7 @@ static int g4x_do_reset(struct intel_gt
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pci_write_config_byte(pdev, I915_GDRST,
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GRDOM_RENDER | GRDOM_RESET_ENABLE);
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- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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if (ret) {
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GT_TRACE(gt, "Wait for render reset failed\n");
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goto out;
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@@ -785,9 +785,7 @@ int __intel_gt_reset(struct intel_gt *gt
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reset_mask = wa_14015076503_start(gt, engine_mask, !retry);
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GT_TRACE(gt, "engine_mask=%x\n", reset_mask);
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- preempt_disable();
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ret = reset(gt, reset_mask, retry);
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- preempt_enable();
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wa_14015076503_end(gt, reset_mask);
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}
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