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@xxxxxxxxx>
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > ---
> > 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.
> > + 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
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.
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_ */
> >
