On 28.06.2021 01:14, 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.
>
> v2:
> (Michal)
> - Use define for H2G room calculations
> - Move INTEL_GUC_SEND_NB define
> (Daniel Vetter)
> - Use msleep_interruptible rather than cond_resched
>
> Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> ---
> .../gt/uc/abi/guc_communication_ctb_abi.h | 3 +-
> drivers/gpu/drm/i915/gt/uc/intel_guc.h | 11 ++-
> drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 90 +++++++++++++++++--
> drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h | 4 +-
> 4 files changed, 94 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h b/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
> index e933ca02d0eb..99e1fad5ca20 100644
> --- a/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
> +++ b/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
> @@ -79,7 +79,8 @@ static_assert(sizeof(struct guc_ct_buffer_desc) == 64);
> * +---+-------+--------------------------------------------------------------+
> */
>
> -#define GUC_CTB_MSG_MIN_LEN 1u
> +#define GUC_CTB_HDR_LEN 1u
> +#define GUC_CTB_MSG_MIN_LEN GUC_CTB_HDR_LEN
if you insist to use dedicated macro for the CTB header len then to be
consistent you need rename header bitfield macros as well, thus
sections/tables will look like:
/**
* DOC: CTB Message
*
* +---+-------+-------------------------------------+
* | | Bits | Description |
* +===+=======+=====================================+
* | 0 | 31:0 | `CTB Header`_ |
* +---+-------+-------------------------------------+
* | 1 | 31:0 | +-------------------------------+ |
* +---+-------+ | | |
* |...| | | CTB Payload | |
* +---+-------+ | | |
* | n | 31:0 | +-------------------------------+ |
* +---+-------+-------------------------------------+
*/
/**
* DOC: CTB Header
*
* +---+-------+-------------------------------------+
* | | Bits | Description |
* +===+=======+=====================================+
* | 0 | 31:16 | **FENCE** - ... |
* | +-------+-------------------------------------+
* | | 15:12 | **FORMAT** - ... |
* | +-------+-------------------------------------+
* | | 11:8 | **RESERVED** |
* | +-------+-------------------------------------+
* | | 7:0 | **NUM_DWORDS** - ... |
* +---+-------+-------------------------------------+
*/
#define GUC_CTB_HDR_0_FENCE (0xffff << 16)
#define GUC_CTB_HDR_0_FORMAT (0xf << 12)
#define GUC_CTB_FORMAT_HXG 0u
#define GUC_CTB_HDR_0_RESERVED (0xf << 8)
#define GUC_CTB_HDR_0_NUM_DWORDS (0xff << 0)
#define GUC_CTB_MAX_DWORDS 255u
#define GUC_CTB_MSG_MIN_LEN GUC_CTB_HDR_LEN
#define GUC_CTB_MSG_MAX_LEN (GUC_CTB_HDR_LEN + GUC_CTB_MAX_DWORDS)
alternatively leave ABI defs as-as and just move your HDR definition out
of ABI headers to inteL_guc_fwif.h as:
#define GUC_CTB_HDR_LEN GUC_CTB_MSG_MIN_LEN
> #define GUC_CTB_MSG_MAX_LEN 256u
> #define GUC_CTB_MSG_0_FENCE (0xffff << 16)
> #define GUC_CTB_MSG_0_FORMAT (0xf << 12)
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> index 4abc59f6f3cd..efc690fc8fb1 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> @@ -74,7 +74,14 @@ 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);
> +}
> +
> +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 +89,7 @@ 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 43e03aa2dde8..90ee95a240e8 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>
these headers should likely be part of patch 5/7
> +
> #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;
> @@ -409,7 +414,7 @@ static int ct_write(struct intel_guc_ct *ct,
> used = tail - head;
^^^^
code above for blocking path is likely calculating free space in old
fashion, while below you are using CIRC_BUF ...
so maybe switch to use circ_buf could be done as separate earlier step
(not part of intro of non-blocking send) so then below use of CIRC_BUF
in non-blocking path will look natural
>
> /* make sure there is a space including extra dw for the fence */
this extra DW is now "header" not just fence
> - if (unlikely(used + len + 1 >= size))
> + if (unlikely(used + len + GUC_CTB_HDR_LEN >= size))
> return -ENOSPC;
>
> /*
> @@ -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]));
>
> CT_DEBUG(ct, "writing (tail %u) %*ph %*ph %*ph\n",
> tail, 4, &header, 4, &hxg, 4 * (len - 1), &action[1]);
> @@ -500,6 +509,48 @@ 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)
why h2g prefix ? function is taking pure *ctb, so maybe:
static bool ctb_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
{ ... }
static bool ct_can_send(struct intel_guc_ct *ct, u32 len_dw)
{
return ctb_has_room(&ct->ctbs.send, len_dw + CTB_HDR_LEN);
}
as we use send/recv, not h2g/g2h and to avoid mistakes add extra header
len here (not by caller - same as in call to ct_write)
> +{
> + 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;
> +}
> +
> +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 + GUC_CTB_HDR_LEN);
> + if (unlikely(!ret)) {
> + ret = -EBUSY;
> + 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,
> @@ -507,8 +558,10 @@ 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;
> + unsigned int sleep_period_ms = 1;
> u32 fence;
> int err;
>
> @@ -516,8 +569,24 @@ 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(&ctb->lock, flags);
> + if (unlikely(!h2g_has_room(ctb, len + GUC_CTB_HDR_LEN))) {
> + spin_unlock_irqrestore(&ctb->lock, flags);
>
> - spin_lock_irqsave(&ct->ctbs.send.lock, flags);
> + if (msleep_interruptible(sleep_period_ms))
> + return -EINTR;
> + sleep_period_ms = sleep_period_ms << 1;
> +
> + goto retry;
> + }
I'm still not convinced that this chunk should be exactly in the same
patch that adds non-blocking path, it's not that with very first use of
one NB call we will hit such problem
so IMHO it can be done earlier, in by anticipating such problem, or
later as fix for potential problem due to stress
note that in the commit message you admitted that new NB variant is not
used yet, so we can't be hit
in other words, try to make patches focused on one item at the time.
>
> fence = ct_get_next_fence(ct);
> request.fence = fence;
> @@ -529,9 +598,9 @@ 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);
> + spin_unlock_irqrestore(&ctb->lock, flags);
>
> if (unlikely(err))
> goto unlink;
> @@ -571,7 +640,7 @@ 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;
> @@ -581,6 +650,9 @@ 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..f6a4d5b33467 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
> @@ -87,8 +86,9 @@ static inline bool intel_guc_ct_enabled(struct intel_guc_ct *ct)
> return ct->enabled;
> }
>
> +#define INTEL_GUC_SEND_NB BIT(31)
INTEL_GUC_CT_SEND_NB ?
^^^^
> 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_ */
>
