[Intel-gfx] [RFC PATCH 36/97] drm/i915/guc: Add non blocking CTB send function
Matthew Brost
matthew.brost at intel.com
Thu May 27 14:35:14 UTC 2021
On Thu, May 27, 2021 at 11:02:24AM +0100, Tvrtko Ursulin wrote:
>
> On 26/05/2021 19:10, Matthew Brost wrote:
>
> [snip]
>
> > > > > > +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 = ctb_has_room(ctb, len + 1);
> > > > > > + 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,
> > > > > > @@ -473,6 +541,7 @@ 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;
> > > > > > @@ -482,8 +551,20 @@ 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();
> > > > >
> > > > > Sleep is just cond_resched below or there is more?
> > > > >
> > > >
> > > > Yes, the cond_resched.
> > > >
> > > > > > + /*
> > > > > > + * 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.
> > > > > > + */
> > > > > > +retry:
> > > > > > spin_lock_irqsave(&ct->ctbs.send.lock, flags);
> > > > > > + if (unlikely(!ctb_has_room(ctb, len + 1))) {
> > > > > > + spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
> > > > > > + cond_resched();
> > > > > > + goto retry;
> > > > > > + }
> > > > >
> > > > > If this patch is about adding a non-blocking send function, and below we can
> > > > > see that it creates a fork:
> > > > >
> > > > > intel_guc_ct_send:
> > > > > ...
> > > > > 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);
> > > > >
> > > > > Then why is there a change in ct_send here, which is not the new
> > > > > non-blocking path?
> > > > >
> > > >
> > > > There is not a change to ct_send(), just to intel_guc_ct_send.
> > >
> > > I was doing by the diff which says:
> > >
> > > static int ct_send(struct intel_guc_ct *ct,
> > > const u32 *action,
> > > u32 len,
> > > @@ -473,6 +541,7 @@ 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;
> > > @@ -482,8 +551,20 @@ 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.
> > > + */
> > > +retry:
> > > spin_lock_irqsave(&ct->ctbs.send.lock, flags);
> > > + if (unlikely(!ctb_has_room(ctb, len + 1))) {
> > > + spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
> > > + cond_resched();
> > > + goto retry;
> > > + }
> > >
> > > So it looks like a change to ct_send to me. Is that wrong?
>
> What about this part - is the patch changing the blocking ct_send or not,
> and if it is why?
>
Yes, ct_send() changes. Sorry for the confusion.
This function needs to be updated to account for the H2G space and
backoff if no space is available.
Matt
> Regards,
>
> Tvrtko
>
>
> > >
> > > Regards,
> > >
> > > Tvrtko
> > >
> > > > As for why intel_guc_ct_send is updated and we don't just a new public
> > > > function, this was another reviewers suggestion. Again can't make
> > > > everyone happy.
> > > > > > fence = ct_get_next_fence(ct);
> > > > > > request.fence = fence;
> > > > > > @@ -495,7 +576,7 @@ 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);
> > > > > > @@ -537,7 +618,7 @@ 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;
> > > > > > @@ -547,6 +628,9 @@ 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..55ef7c52472f 100644
> > > > > > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> > > > > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> > > > > > @@ -9,6 +9,7 @@
> > > > > > #include <linux/interrupt.h>
> > > > > > #include <linux/spinlock.h>
> > > > > > #include <linux/workqueue.h>
> > > > > > +#include <linux/ktime.h>
> > > > > > #include "intel_guc_fwif.h"
> > > > > > @@ -42,7 +43,6 @@ 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
> > > > > > @@ -69,6 +69,9 @@ struct intel_guc_ct {
> > > > > > struct list_head incoming; /* incoming requests */
> > > > > > struct work_struct worker; /* handler for incoming requests */
> > > > > > } requests;
> > > > > > +
> > > > > > + /** @stall_time: time of first time a CTB submission is stalled */
> > > > > > + ktime_t stall_time;
> > > > >
> > > > > Unused in this patch.
> > > > >
> > > >
> > > > Yea, wrong patch. Will fix.
> > > >
> > > > Matt
> > > > > > };
> > > > > > void intel_guc_ct_init_early(struct intel_guc_ct *ct);
> > > > > > @@ -88,7 +91,7 @@ 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_ */
> > > > > >
> > > > >
> > > > > Regards,
> > > > >
> > > > > Tvrtko
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