Re: [Intel-gfx] [PATCH 04/47] drm/i915/guc: Add non blocking CTB send function

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

On Fri, Jun 25, 2021 at 01:50:21PM +0200, Michal Wajdeczko wrote:
> 
> 
> On 25.06.2021 00:41, Matthew Brost wrote:
> > On Thu, Jun 24, 2021 at 07:02:18PM +0200, Michal Wajdeczko wrote:
> >>
> >>
> >> On 24.06.2021 17:49, Matthew Brost wrote:
> >>> On Thu, Jun 24, 2021 at 04:48:32PM +0200, Michal Wajdeczko wrote:
> >>>>
> >>>>
> >>>> On 24.06.2021 09:04, Matthew Brost wrote:
> >>>>> Add non blocking CTB send function, intel_guc_send_nb. GuC submission
> >>>>> will send CTBs in the critical path and does not need to wait for these
> >>>>> CTBs to complete before moving on, hence the need for this new function.
> >>>>>
> >>>>> The non-blocking CTB now must have a flow control mechanism to ensure
> >>>>> the buffer isn't overrun. A lazy spin wait is used as we believe the
> >>>>> flow control condition should be rare with a properly sized buffer.
> >>>>>
> >>>>> The function, intel_guc_send_nb, is exported in this patch but unused.
> >>>>> Several patches later in the series make use of this function.
> >>>>>
> >>>>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> >>>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> >>>>> ---
> >>>>>  drivers/gpu/drm/i915/gt/uc/intel_guc.h    | 12 +++-
> >>>>>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 77 +++++++++++++++++++++--
> >>>>>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h |  3 +-
> >>>>>  3 files changed, 82 insertions(+), 10 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> >>>>> index 4abc59f6f3cd..24b1df6ad4ae 100644
> >>>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> >>>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> >>>>> @@ -74,7 +74,15 @@ static inline struct intel_guc *log_to_guc(struct intel_guc_log *log)
> >>>>>  static
> >>>>>  inline int intel_guc_send(struct intel_guc *guc, const u32 *action, u32 len)
> >>>>>  {
> >>>>> -	return intel_guc_ct_send(&guc->ct, action, len, NULL, 0);
> >>>>> +	return intel_guc_ct_send(&guc->ct, action, len, NULL, 0, 0);
> >>>>> +}
> >>>>> +
> >>>>> +#define INTEL_GUC_SEND_NB		BIT(31)
> >>>>
> >>>> hmm, this flag really belongs to intel_guc_ct_send() so it should be
> >>>> defined as CTB flag near that function declaration
> >>>>
> >>>
> >>> I can move this up a few lines.
> >>>
> >>>>> +static
> >>>>> +inline int intel_guc_send_nb(struct intel_guc *guc, const u32 *action, u32 len)
> >>>>> +{
> >>>>> +	return intel_guc_ct_send(&guc->ct, action, len, NULL, 0,
> >>>>> +				 INTEL_GUC_SEND_NB);
> >>>>>  }
> >>>>>  
> >>>>>  static inline int
> >>>>> @@ -82,7 +90,7 @@ intel_guc_send_and_receive(struct intel_guc *guc, const u32 *action, u32 len,
> >>>>>  			   u32 *response_buf, u32 response_buf_size)
> >>>>>  {
> >>>>>  	return intel_guc_ct_send(&guc->ct, action, len,
> >>>>> -				 response_buf, response_buf_size);
> >>>>> +				 response_buf, response_buf_size, 0);
> >>>>>  }
> >>>>>  
> >>>>>  static inline void intel_guc_to_host_event_handler(struct intel_guc *guc)
> >>>>> 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 a17215920e58..c9a65d05911f 100644
> >>>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> >>>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> >>>>> @@ -3,6 +3,11 @@
> >>>>>   * Copyright © 2016-2019 Intel Corporation
> >>>>>   */
> >>>>>  
> >>>>> +#include <linux/circ_buf.h>
> >>>>> +#include <linux/ktime.h>
> >>>>> +#include <linux/time64.h>
> >>>>> +#include <linux/timekeeping.h>
> >>>>> +
> >>>>>  #include "i915_drv.h"
> >>>>>  #include "intel_guc_ct.h"
> >>>>>  #include "gt/intel_gt.h"
> >>>>> @@ -373,7 +378,7 @@ static void write_barrier(struct intel_guc_ct *ct)
> >>>>>  static int ct_write(struct intel_guc_ct *ct,
> >>>>>  		    const u32 *action,
> >>>>>  		    u32 len /* in dwords */,
> >>>>> -		    u32 fence)
> >>>>> +		    u32 fence, u32 flags)
> >>>>>  {
> >>>>>  	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
> >>>>>  	struct guc_ct_buffer_desc *desc = ctb->desc;
> >>>>> @@ -421,9 +426,13 @@ static int ct_write(struct intel_guc_ct *ct,
> >>>>>  		 FIELD_PREP(GUC_CTB_MSG_0_NUM_DWORDS, len) |
> >>>>>  		 FIELD_PREP(GUC_CTB_MSG_0_FENCE, fence);
> >>>>>  
> >>>>> -	hxg = FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_REQUEST) |
> >>>>> -	      FIELD_PREP(GUC_HXG_REQUEST_MSG_0_ACTION |
> >>>>> -			 GUC_HXG_REQUEST_MSG_0_DATA0, action[0]);
> >>>>> +	hxg = (flags & INTEL_GUC_SEND_NB) ?
> >>>>> +		(FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_EVENT) |
> >>>>> +		 FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
> >>>>> +			    GUC_HXG_EVENT_MSG_0_DATA0, action[0])) :
> >>>>> +		(FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_REQUEST) |
> >>>>> +		 FIELD_PREP(GUC_HXG_REQUEST_MSG_0_ACTION |
> >>>>> +			    GUC_HXG_REQUEST_MSG_0_DATA0, action[0]));
> >>>>
> >>>> or as we already switched to accept and return whole HXG messages in
> >>>> guc_send_mmio() maybe we should do the same for CTB variant too and
> >>>> instead of using extra flag just let caller to prepare proper HXG header
> >>>> with HXG_EVENT type and then in CTB code just look at this type to make
> >>>> decision which code path to use
> >>>>
> >>>
> >>> Not sure I follow. Anyways could this be done in a follow up by you if
> >>> want this change.
> >>>  
> >>>> note that existing callers should not be impacted, as full HXG header
> >>>> for the REQUEST message looks exactly the same as "action" code alone.
> >>>>
> >>>>>  
> >>>>>  	CT_DEBUG(ct, "writing (tail %u) %*ph %*ph %*ph\n",
> >>>>>  		 tail, 4, &header, 4, &hxg, 4 * (len - 1), &action[1]);
> >>>>> @@ -498,6 +507,46 @@ static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
> >>>>>  	return err;
> >>>>>  }
> >>>>>  
> >>>>> +static inline bool h2g_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
> >>>>> +{
> >>>>> +	struct guc_ct_buffer_desc *desc = ctb->desc;
> >>>>> +	u32 head = READ_ONCE(desc->head);
> >>>>> +	u32 space;
> >>>>> +
> >>>>> +	space = CIRC_SPACE(desc->tail, head, ctb->size);
> >>>>> +
> >>>>> +	return space >= len_dw;
> >>>>
> >>>> here you are returning true(1) as has room
> >>>>
> >>>
> >>> See below.
> >>>  
> >>>>> +}
> >>>>> +
> >>>>> +static int ct_send_nb(struct intel_guc_ct *ct,
> >>>>> +		      const u32 *action,
> >>>>> +		      u32 len,
> >>>>> +		      u32 flags)
> >>>>> +{
> >>>>> +	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
> >>>>> +	unsigned long spin_flags;
> >>>>> +	u32 fence;
> >>>>> +	int ret;
> >>>>> +
> >>>>> +	spin_lock_irqsave(&ctb->lock, spin_flags);
> >>>>> +
> >>>>> +	ret = h2g_has_room(ctb, len + 1);
> >>>>
> >>>> but here you treat "1" it as en error
> >>>>
> >>>
> >>> Yes, this patch is broken but fixed in a follow up one. Regardless I'll
> >>> fix this patch in place.
> >>>
> >>>> and this "1" is GUC_HXG_MSG_MIN_LEN, right ?
> >>>>
> >>>
> >>> Not exactly. This is following how ct_send() uses the action + len
> >>> field. Action[0] field goes in the HXG header and extra + 1 is for the
> >>> CT header.
> >>
> >> well, "len" already counts "action" so by treating input as full HXG
> >> message (including HXG header) will make it cleaner
> >>
> > 
> > Yes, I know. See above. To me GUC_HXG_MSG_MIN_LEN makes zero sense and
> > it is worse than adding + 1. This + 1 accounts for the CT header not the
> > HXG header. If any we add a new define, GUC_CT_HDR_LEN, and add that.
> 
> you mean GUC_CTB_MSG_MIN_LEN ? it's already there [1]
> 

Kinda? I think we should have a define GUC_CTB_HDR_LEN which is 1 and
GUC_CTB_MSG_MIN_LEN is defined as GUC_CTB_HDR_LEN. 'GUC_CTB_HDR_LEN'
makes it clear that the + 1 is referring to the header. I've done this
branch of these patches already.

Matt

> [1]
> https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h#n82
> 
> > 
> > Matt
> > 
> >> we can try do it later but by doing it right now we would avoid
> >> introducing this send_nb() function and deprecating them long term again
> >>
> >>>
> >>>>> +	if (unlikely(ret))
> >>>>> +		goto out;
> >>>>> +
> >>>>> +	fence = ct_get_next_fence(ct);
> >>>>> +	ret = ct_write(ct, action, len, fence, flags);
> >>>>> +	if (unlikely(ret))
> >>>>> +		goto out;
> >>>>> +
> >>>>> +	intel_guc_notify(ct_to_guc(ct));
> >>>>> +
> >>>>> +out:
> >>>>> +	spin_unlock_irqrestore(&ctb->lock, spin_flags);
> >>>>> +
> >>>>> +	return ret;
> >>>>> +}
> >>>>> +
> >>>>>  static int ct_send(struct intel_guc_ct *ct,
> >>>>>  		   const u32 *action,
> >>>>>  		   u32 len,
> >>>>> @@ -505,6 +554,7 @@ static int ct_send(struct intel_guc_ct *ct,
> >>>>>  		   u32 response_buf_size,
> >>>>>  		   u32 *status)
> >>>>>  {
> >>>>> +	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
> >>>>>  	struct ct_request request;
> >>>>>  	unsigned long flags;
> >>>>>  	u32 fence;
> >>>>> @@ -514,8 +564,20 @@ static int ct_send(struct intel_guc_ct *ct,
> >>>>>  	GEM_BUG_ON(!len);
> >>>>>  	GEM_BUG_ON(len & ~GUC_CT_MSG_LEN_MASK);
> >>>>>  	GEM_BUG_ON(!response_buf && response_buf_size);
> >>>>> +	might_sleep();
> >>>>>  
> >>>>> +	/*
> >>>>> +	 * We use a lazy spin wait loop here as we believe that if the CT
> >>>>> +	 * buffers are sized correctly the flow control condition should be
> >>>>> +	 * rare.
> >>>>
> >>>> shouldn't we at least try to log such cases with RATE_LIMITED to find
> >>>> out how "rare" it is, or if really unlikely just return -EBUSY as in
> >>>> case of non-blocking send ?
> >>>>
> >>>
> >>> Definitely not return -EBUSY as this a blocking call. Perhaps we can log
> >>
> >> blocking calls still can fail for various reasons, full CTB is one of
> >> them, and if we return error (now broken) for non-blocking variant then
> >> we should do the same for blocking variant as well and let the caller
> >> decide about next steps
> >>
> >>> this, but IGTs likely can hit rather easily. It really is only
> >>> interesting if real workloads hit this. Regardless that can be a follow
> >>> up.
> >>
> >> if we hide retry in a silent loop then we will not find it out if we hit
> >> this condition (IGT or real WL) or not
> >>
> >>>
> >>> Matt
> >>>  
> >>>>> +	 */
> >>>>> +retry:
> >>>>>  	spin_lock_irqsave(&ct->ctbs.send.lock, flags);
> >>>>> +	if (unlikely(!h2g_has_room(ctb, len + 1))) {
> >>>>> +		spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
> >>>>> +		cond_resched();
> >>>>> +		goto retry;
> >>>>> +	}
> >>>>>  
> >>>>>  	fence = ct_get_next_fence(ct);
> >>>>>  	request.fence = fence;
> >>>>> @@ -527,7 +589,7 @@ static int ct_send(struct intel_guc_ct *ct,
> >>>>>  	list_add_tail(&request.link, &ct->requests.pending);
> >>>>>  	spin_unlock(&ct->requests.lock);
> >>>>>  
> >>>>> -	err = ct_write(ct, action, len, fence);
> >>>>> +	err = ct_write(ct, action, len, fence, 0);
> >>>>>  
> >>>>>  	spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
> >>>>>  
> >>>>> @@ -569,7 +631,7 @@ static int ct_send(struct intel_guc_ct *ct,
> >>>>>   * Command Transport (CT) buffer based GuC send function.
> >>>>>   */
> >>>>>  int intel_guc_ct_send(struct intel_guc_ct *ct, const u32 *action, u32 len,
> >>>>> -		      u32 *response_buf, u32 response_buf_size)
> >>>>> +		      u32 *response_buf, u32 response_buf_size, u32 flags)
> >>>>>  {
> >>>>>  	u32 status = ~0; /* undefined */
> >>>>>  	int ret;
> >>>>> @@ -579,6 +641,9 @@ int intel_guc_ct_send(struct intel_guc_ct *ct, const u32 *action, u32 len,
> >>>>>  		return -ENODEV;
> >>>>>  	}
> >>>>>  
> >>>>> +	if (flags & INTEL_GUC_SEND_NB)
> >>>>> +		return ct_send_nb(ct, action, len, flags);
> >>>>> +
> >>>>>  	ret = ct_send(ct, action, len, response_buf, response_buf_size, &status);
> >>>>>  	if (unlikely(ret < 0)) {
> >>>>>  		CT_ERROR(ct, "Sending action %#x failed (err=%d status=%#X)\n",
> >>>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> >>>>> index 1ae2dde6db93..eb69263324ba 100644
> >>>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> >>>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> >>>>> @@ -42,7 +42,6 @@ struct intel_guc_ct_buffer {
> >>>>>  	bool broken;
> >>>>>  };
> >>>>>  
> >>>>> -
> >>>>>  /** Top-level structure for Command Transport related data
> >>>>>   *
> >>>>>   * Includes a pair of CT buffers for bi-directional communication and tracking
> >>>>> @@ -88,7 +87,7 @@ static inline bool intel_guc_ct_enabled(struct intel_guc_ct *ct)
> >>>>>  }
> >>>>>  
> >>>>>  int intel_guc_ct_send(struct intel_guc_ct *ct, const u32 *action, u32 len,
> >>>>> -		      u32 *response_buf, u32 response_buf_size);
> >>>>> +		      u32 *response_buf, u32 response_buf_size, u32 flags);
> >>>>>  void intel_guc_ct_event_handler(struct intel_guc_ct *ct);
> >>>>>  
> >>>>>  #endif /* _INTEL_GUC_CT_H_ */
> >>>>>