Re: [PATCH] drm/i915: Take runtime pm reference on hangcheck_info

Daniel Vetter
2015-02-05T14:28:24Z

On Thu, Feb 05, 2015 at 12:16:32PM +0200, Mika Kuoppala wrote:
> We read the coherent current seqno and actual head from ring.
> For hardware access we need to take runtime_pm reference, which brings in
> locking. As this debugfs entry is for debugging hangcheck behaviour,
> including locking problems, we need to be flexible on taking them.
>
> Try to see if we get a lock and if so, get seqno and actual head
> from hardware. If we don't have exclusive access, get lazy coherent
> seqno and print token acthd for which the user can see that the
> seqno is of different nature.
>
> Testcase: igt/pm_rpm/debugfs-read
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88910
> Tested-by: Ding Heng <hengx.ding@intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
> drivers/gpu/drm/i915/i915_debugfs.c | 26 +++++++++++++++++++++++---
> 1 file changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 9af17fb..5a6b0e2 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1223,8 +1223,11 @@ out:
> static int i915_hangcheck_info(struct seq_file *m, void *unused)
> {
> struct drm_info_node *node = m->private;
> - struct drm_i915_private *dev_priv = to_i915(node->minor->dev);
> + struct drm_device *dev = node->minor->dev;
> + struct drm_i915_private *dev_priv = dev->dev_private;
> struct intel_engine_cs *ring;
> + u64 acthd[I915_NUM_RINGS];
> + u32 seqno[I915_NUM_RINGS];
> int i;
>
> if (!i915.enable_hangcheck) {
> @@ -1232,6 +1235,23 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
> return 0;
> }
>
> + if (mutex_trylock(&dev->struct_mutex)) {

Why do we need dev->struct_mutex here?
-Daniel

> + intel_runtime_pm_get(dev_priv);
> +
> + for_each_ring(ring, dev_priv, i) {
> + seqno[i] = ring->get_seqno(ring, false);
> + acthd[i] = intel_ring_get_active_head(ring);
> + }
> +
> + intel_runtime_pm_put(dev_priv);
> + mutex_unlock(&dev->struct_mutex);
> + } else {
> + for_each_ring(ring, dev_priv, i) {
> + seqno[i] = ring->get_seqno(ring, true);
> + acthd[i] = -1;
> + }
> + }
> +
> if (delayed_work_pending(&dev_priv->gpu_error.hangcheck_work)) {
> seq_printf(m, "Hangcheck active, fires in %dms\n",
> jiffies_to_msecs(dev_priv->gpu_error.hangcheck_work.timer.expires -
> @@ -1242,12 +1262,12 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
> for_each_ring(ring, dev_priv, i) {
> seq_printf(m, "%s:\n", ring->name);
> seq_printf(m, "\tseqno = %x [current %x]\n",
> - ring->hangcheck.seqno, ring->get_seqno(ring, false));
> + ring->hangcheck.seqno, seqno[i]);
> seq_printf(m, "\taction = %d\n", ring->hangcheck.action);
> seq_printf(m, "\tscore = %d\n", ring->hangcheck.score);
> seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
> (long long)ring->hangcheck.acthd,
> - (long long)intel_ring_get_active_head(ring));
> + (long long)acthd[i]);
> seq_printf(m, "\tmax ACTHD = 0x%08llx\n",
> (long long)ring->hangcheck.max_acthd);
> }
> --
> 1.9.1
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch