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

Mika Kuoppala
2015-02-05T15:54:50Z

Daniel Vetter <daniel@ffwll.ch> writes:

> 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?

Apparently intel_runtime_pm_get is fine without it. Cargoculted
from the neighbouring debugfs entry.

Only thing I can think of is that it reveals if we had
exclusive access depending of achtd token value printed. But is
that information then of any use I dont know.

I'll respin

-Mika

> -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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>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch