Re: [Intel-gfx] [PATCH 13/20] drm/i915/guc: Relax CTB response timeout

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Jun 04, 2021 at 10:33:07AM +0200, Daniel Vetter wrote:
> On Wed, Jun 02, 2021 at 10:16:23PM -0700, Matthew Brost wrote:
> > From: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > 
> > In upcoming patch we will allow more CTB requests to be sent in
> > parallel to the GuC for processing, so we shouldn't assume any more
> > that GuC will always reply without 10ms.
> > 
> > Use bigger value from CONFIG_DRM_I915_GUC_CTB_TIMEOUT instead.
> > 
> > v2: Add CONFIG_DRM_I915_GUC_CTB_TIMEOUT config option
> > 
> > Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > Reviewed-by: Matthew Brost <matthew.brost@intel.com>
> 
> So this is a rant, but for upstream we really need to do better than
> internal:
> 
> - The driver must work by default in the optimal configuration.
> 
> - Any config change that we haven't validated _must_ taint the kernel
>   (this is especially for module options, but also for config settings)
> 
> - Config need a real reason beyond "was useful for bring-up".
> 
> Our internal tree is an absolute disaster right now, with multi-line
> kernel configs (different on each platform) and bespoke kernel config or
> the driver just fails. We're the expert on our own hw, we should know how
> it works, not offload that to users essentially asking them "how shitty do
> you think Intel hw is in responding timely".
> 
> Yes I know there's a lot of these there already, they don't make a lot of
> sense either.
> 
> Except if there's a real reason for this (aside from us just offloading
> testing to our users instead of doing it ourselves properly) I think we
> should hardcode this, with a comment explaining why. Maybe with a switch
> between the PF/VF case once that's landed.
> 
> > ---
> >  drivers/gpu/drm/i915/Kconfig.profile      | 10 ++++++++++
> >  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c |  5 ++++-
> >  2 files changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/Kconfig.profile b/drivers/gpu/drm/i915/Kconfig.profile
> > index 39328567c200..0d5475b5f28a 100644
> > --- a/drivers/gpu/drm/i915/Kconfig.profile
> > +++ b/drivers/gpu/drm/i915/Kconfig.profile
> > @@ -38,6 +38,16 @@ config DRM_I915_USERFAULT_AUTOSUSPEND
> >  	  May be 0 to disable the extra delay and solely use the device level
> >  	  runtime pm autosuspend delay tunable.
> >  
> > +config DRM_I915_GUC_CTB_TIMEOUT
> > +	int "How long to wait for the GuC to make forward progress on CTBs (ms)"
> > +	default 1500 # milliseconds
> > +	range 10 60000
> 
> Also range is definitely off, drm/scheduler will probably nuke you
> beforehand :-)
> 
> That's kinda another issue I have with all these kconfig knobs: Maybe we
> need a knob for "relax with reset attempts, my workloads overload my gpus
> routinely", which then scales _all_ timeouts proportionally. But letting
> the user set them all, with silly combiniations like resetting the
> workload before heartbeat or stuff like that doesn't make much sense.
>

Yes, the code as is the user could do some wacky stuff that doesn't make
sense at all.
 
> Anyway, tiny patch so hopefully I can leave this one out for now until
> we've closed this.

No issue leaving this out as blocking CTBs are never really used anyways
until SRIOV aside from setup / debugging. That being said, we might
still want a higher hardcoded value in the meantime, perhaps around a
second. I can follow up on that if needed.

Matt

> -Daniel
> 
> > +	help
> > +	  Configures the default timeout waiting for GuC the to make forward
> > +	  progress on CTBs. e.g. Waiting for a response to a requeset.
> > +
> > +	  A range of 10 ms to 60000 ms is allowed.
> > +
> >  config DRM_I915_HEARTBEAT_INTERVAL
> >  	int "Interval between heartbeat pulses (ms)"
> >  	default 2500 # milliseconds
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > index 916c2b80c841..cf1fb09ef766 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > @@ -436,6 +436,7 @@ static int ct_write(struct intel_guc_ct *ct,
> >   */
> >  static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
> >  {
> > +	long timeout;
> >  	int err;
> >  
> >  	/*
> > @@ -443,10 +444,12 @@ static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
> >  	 * up to that length of time, then switch to a slower sleep-wait loop.
> >  	 * No GuC command should ever take longer than 10ms.
> >  	 */
> > +	timeout = CONFIG_DRM_I915_GUC_CTB_TIMEOUT;
> > +
> >  #define done INTEL_GUC_MSG_IS_RESPONSE(READ_ONCE(req->status))
> >  	err = wait_for_us(done, 10);
> >  	if (err)
> > -		err = wait_for(done, 10);
> > +		err = wait_for(done, timeout);
> >  #undef done
> >  
> >  	if (unlikely(err))
> > -- 
> > 2.28.0
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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