[Intel-gfx] [PATCH v2 2/2] drm/i915/scheduler: add gvt notification for guc

[Dong, Chuanxiao]

> -----Original Message-----
> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> Sent: Thursday, April 6, 2017 11:07 PM
> To: Dong, Chuanxiao
> Cc: intel-gfx at lists.freedesktop.org; intel-gvt-dev at lists.freedesktop.org;
> Zheng, Xiao; Tian, Kevin; joonas.lahtinen at linux.intel.com; Wang, Zhi A
> Subject: Re: [PATCH v2 2/2] drm/i915/scheduler: add gvt notification for guc
> 
> On Thu, Apr 06, 2017 at 02:49:54PM +0000, Dong, Chuanxiao wrote:
> >
> >
> > > -----Original Message-----
> > > From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> > > Sent: Thursday, April 6, 2017 10:19 PM
> > > To: Dong, Chuanxiao
> > > Cc: intel-gfx at lists.freedesktop.org;
> > > intel-gvt-dev at lists.freedesktop.org;
> > > Zheng, Xiao; Tian, Kevin; joonas.lahtinen at linux.intel.com
> > > Subject: Re: [PATCH v2 2/2] drm/i915/scheduler: add gvt notification
> > > for guc
> > >
> > > On Thu, Apr 06, 2017 at 02:05:15PM +0000, Dong, Chuanxiao wrote:
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> > > > > Sent: Thursday, April 6, 2017 9:32 PM
> > > > > To: Dong, Chuanxiao
> > > > > Cc: intel-gfx at lists.freedesktop.org;
> > > > > intel-gvt-dev at lists.freedesktop.org;
> > > > > Zheng, Xiao; Tian, Kevin; joonas.lahtinen at linux.intel.com
> > > > > Subject: Re: [PATCH v2 2/2] drm/i915/scheduler: add gvt
> > > > > notification for guc
> > > > >
> > > > > On Tue, Mar 28, 2017 at 05:38:41PM +0800, Chuanxiao Dong wrote:
> > > > > > GVT request needs a manual mmio load/restore. Before GuC
> > > > > > submit a request, send notification to gvt for mmio loading.
> > > > > > And after the GuC finished this GVT request, notify gvt again for
> mmio restore.
> > > > > > This follows the usage when using execlists submission.
> > > > > >
> > > > > > Cc: xiao.zheng at intel.com
> > > > > > Cc: kevin.tian at intel.com
> > > > > > Cc: joonas.lahtinen at linux.intel.com
> > > > > > Cc: chris at chris-wilson.co.uk
> > > > > > Signed-off-by: Chuanxiao Dong <chuanxiao.dong at intel.com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/i915/i915_guc_submission.c |  4 ++++
> > > > > >  drivers/gpu/drm/i915/intel_gvt.h           | 12 ++++++++++++
> > > > > >  drivers/gpu/drm/i915/intel_lrc.c           | 21 +++------------------
> > > > > >  3 files changed, 19 insertions(+), 18 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c
> > > > > > b/drivers/gpu/drm/i915/i915_guc_submission.c
> > > > > > index 58087630..d8a5942 100644
> > > > > > --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> > > > > > +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> > > > > > @@ -606,6 +606,8 @@ static void __i915_guc_submit(struct
> > > > > drm_i915_gem_request *rq)
> > > > > >  	unsigned long flags;
> > > > > >  	int b_ret;
> > > > > >
> > > > > > +	intel_gvt_notify_context_status(rq,
> > > > > > +INTEL_CONTEXT_SCHEDULE_IN);
> > > > > > +
> > > > > >  	/* WA to flush out the pending GMADR writes to ring buffer.
> */
> > > > > >  	if (i915_vma_is_map_and_fenceable(rq->ring->vma))
> > > > > >  		POSTING_READ_FW(GUC_STATUS); @@ -725,6
> +727,8 @@ static
> > > > > > void i915_guc_irq_handler(unsigned long
> > > data)
> > > > > >  		rq = port[0].request;
> > > > > >  		while (rq && i915_gem_request_completed(rq)) {
> > > > > >  			trace_i915_gem_request_out(rq);
> > > > > > +			intel_gvt_notify_context_status(rq,
> > > > > > +
> 	INTEL_CONTEXT_SCHEDULE_OUT);
> > > > >
> > > > > This is incorrect though. This is no better than just waiting
> > > > > for the request, which is not enough since the idea is that you
> > > > > need to wait for the context image to be completely written to
> > > > > memory before
> > > you read it.
> > > > > -Chris
> > > >
> > > > The wait for the context image to be completely written will be
> > > > done in the
> > > notification from the GVT, by checking the CSB. If put the wait here
> > > will made each i915 request to wait, which seems not necessary.
> > >
> > > Urm, no. I hope you mean the wait will be on some other thread than
> > > inside this interrupt handler.
> >
> > The SCHEDULE_OUT means to stop GuC to submit another request before
> the current one is completed by GVT so GVT can manually restore the MMIO.
> So this irq handler should wait until SCHEDULE_OUT is completed. How it
> possible to make this irq handler to wait for another thread? From the
> current software architecture there is no other thread....
> 
> No. It is not acceptable to have any blocking here. Rather you delegate the
> polling of CSB to a thread/worker that you kick off from this notify.
> -Chris

The major issue is that we should wait for the context image to be completely written to memory before GVT read it. I will double check if we are really reading from context image in this SCHEDULE_OUT event and return back later.

Thanks
Chuanxiao

> 
> --
> Chris Wilson, Intel Open Source Technology Centre