On 06.07.2021 21:00, John Harrison wrote:
> On 7/1/2021 10:15, Matthew Brost wrote:
>> CTB writes are now in the path of command submission and should be
>> optimized for performance. Rather than reading CTB descriptor values
>> (e.g. head, tail) which could result in accesses across the PCIe bus,
>> store shadow local copies and only read/write the descriptor values when
>> absolutely necessary. Also store the current space in the each channel
>> locally.
>>
>> v2:
>> (Michel)
>> - Add additional sanity checks for head / tail pointers
>> - Use GUC_CTB_HDR_LEN rather than magic 1
>>
>> 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_ct.c | 88 +++++++++++++++--------
>> drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h | 6 ++
>> 2 files changed, 65 insertions(+), 29 deletions(-)
>>
>> 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 a9cb7b608520..5b8b4ff609e2 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>> @@ -130,6 +130,10 @@ static void guc_ct_buffer_desc_init(struct
>> guc_ct_buffer_desc *desc)
>> static void guc_ct_buffer_reset(struct intel_guc_ct_buffer *ctb)
>> {
>> ctb->broken = false;
>> + ctb->tail = 0;
>> + ctb->head = 0;
>> + ctb->space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size);
>> +
>> guc_ct_buffer_desc_init(ctb->desc);
>> }
>> @@ -383,10 +387,8 @@ static int ct_write(struct intel_guc_ct *ct,
>> {
>> struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
>> struct guc_ct_buffer_desc *desc = ctb->desc;
>> - u32 head = desc->head;
>> - u32 tail = desc->tail;
>> + u32 tail = ctb->tail;
>> u32 size = ctb->size;
>> - u32 used;
>> u32 header;
>> u32 hxg;
>> u32 *cmds = ctb->cmds;
>> @@ -395,25 +397,22 @@ static int ct_write(struct intel_guc_ct *ct,
>> if (unlikely(desc->status))
>> goto corrupted;
>> - if (unlikely((tail | head) >= size)) {
>> + GEM_BUG_ON(tail > size);
>> +
>> +#ifdef CONFIG_DRM_I915_DEBUG_GUC
>> + if (unlikely(tail != READ_ONCE(desc->tail))) {
>> + CT_ERROR(ct, "Tail was modified %u != %u\n",
>> + desc->tail, ctb->tail);
>> + desc->status |= GUC_CTB_STATUS_MISMATCH;
>> + goto corrupted;
>> + }
>> + if (unlikely((desc->tail | desc->head) >= size)) {
>> CT_ERROR(ct, "Invalid offsets head=%u tail=%u (size=%u)\n",
>> - head, tail, size);
>> + desc->head, desc->tail, size);
>> desc->status |= GUC_CTB_STATUS_OVERFLOW;
>> goto corrupted;
>> }
>> -
>> - /*
>> - * tail == head condition indicates empty. GuC FW does not support
>> - * using up the entire buffer to get tail == head meaning full.
>> - */
>> - if (tail < head)
>> - used = (size - head) + tail;
>> - else
>> - used = tail - head;
>> -
>> - /* make sure there is a space including extra dw for the fence */
>> - if (unlikely(used + len + GUC_CTB_HDR_LEN >= size))
>> - return -ENOSPC;
>> +#endif
>> /*
>> * dw0: CT header (including fence)
>> @@ -454,7 +453,9 @@ static int ct_write(struct intel_guc_ct *ct,
>> write_barrier(ct);
>> /* now update descriptor */
>> + ctb->tail = tail;
>> WRITE_ONCE(desc->tail, tail);
>> + ctb->space -= len + GUC_CTB_HDR_LEN;
>> return 0;
>> @@ -470,7 +471,7 @@ static int ct_write(struct intel_guc_ct *ct,
>> * @req: pointer to pending request
>> * @status: placeholder for status
>> *
>> - * For each sent request, Guc shall send bac CT response message.
>> + * For each sent request, GuC shall send back CT response message.
>> * Our message handler will update status of tracked request once
>> * response message with given fence is received. Wait here and
>> * check for valid response status value.
>> @@ -526,24 +527,35 @@ static inline bool ct_deadlocked(struct
>> intel_guc_ct *ct)
>> return ret;
>> }
>> -static inline bool h2g_has_room(struct intel_guc_ct_buffer *ctb,
>> u32 len_dw)
>> +static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
>> {
>> - struct guc_ct_buffer_desc *desc = ctb->desc;
>> - u32 head = READ_ONCE(desc->head);
>> + struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
>> + u32 head;
>> u32 space;
>> - space = CIRC_SPACE(desc->tail, head, ctb->size);
>> + if (ctb->space >= len_dw)
>> + return true;
>> +
>> + head = READ_ONCE(ctb->desc->head);
>> + if (unlikely(head > ctb->size)) {
>> + CT_ERROR(ct, "Corrupted descriptor head=%u tail=%u size=%u\n",
>> + ctb->desc->head, ctb->desc->tail, ctb->size);
>> + ctb->desc->status |= GUC_CTB_STATUS_OVERFLOW;
>> + ctb->broken = true;
>> + return false;
>> + }
>> +
>> + space = CIRC_SPACE(ctb->tail, head, ctb->size);
>> + ctb->space = space;
>> return space >= len_dw;
>> }
>> static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
>> {
>> - struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
>> -
>> lockdep_assert_held(&ct->ctbs.send.lock);
>> - if (unlikely(!h2g_has_room(ctb, len_dw))) {
>> + if (unlikely(!h2g_has_room(ct, len_dw))) {
>> if (ct->stall_time == KTIME_MAX)
>> ct->stall_time = ktime_get();
>> @@ -613,7 +625,7 @@ static int ct_send(struct intel_guc_ct *ct,
>> */
>> retry:
>> spin_lock_irqsave(&ctb->lock, flags);
>> - if (unlikely(!h2g_has_room(ctb, len + GUC_CTB_HDR_LEN))) {
>> + if (unlikely(!h2g_has_room(ct, len + GUC_CTB_HDR_LEN))) {
>> if (ct->stall_time == KTIME_MAX)
>> ct->stall_time = ktime_get();
>> spin_unlock_irqrestore(&ctb->lock, flags);
>> @@ -733,7 +745,7 @@ static int ct_read(struct intel_guc_ct *ct, struct
>> ct_incoming_msg **msg)
>> {
>> struct intel_guc_ct_buffer *ctb = &ct->ctbs.recv;
>> struct guc_ct_buffer_desc *desc = ctb->desc;
>> - u32 head = desc->head;
>> + u32 head = ctb->head;
>> u32 tail = desc->tail;
>> u32 size = ctb->size;
>> u32 *cmds = ctb->cmds;
>> @@ -748,12 +760,29 @@ static int ct_read(struct intel_guc_ct *ct,
>> struct ct_incoming_msg **msg)
>> if (unlikely(desc->status))
>> goto corrupted;
>> - if (unlikely((tail | head) >= size)) {
>> + GEM_BUG_ON(head > size);
> Is the BUG_ON necessary given that both options below do the same check
> but as a corrupted buffer test (with subsequent recovery by GT reset?)
> rather than killing the driver.
"head" and "size" are now fully owned by the driver.
BUGON here is to make sure driver is coded correctly.
>
>> +
>> +#ifdef CONFIG_DRM_I915_DEBUG_GUC
>> + if (unlikely(head != READ_ONCE(desc->head))) {
>> + CT_ERROR(ct, "Head was modified %u != %u\n",
>> + desc->head, ctb->head);
>> + desc->status |= GUC_CTB_STATUS_MISMATCH;
>> + goto corrupted;
>> + }
>> + if (unlikely((desc->tail | desc->head) >= size)) {
>> + CT_ERROR(ct, "Invalid offsets head=%u tail=%u (size=%u)\n",
>> + head, tail, size);
>> + desc->status |= GUC_CTB_STATUS_OVERFLOW;
>> + goto corrupted;
>> + }
>> +#else
>> + if (unlikely((tail | ctb->head) >= size)) {
> Could just be 'head' rather than 'ctb->head'.
or drop "ctb->head" completely since this is driver owned field and
above you already have BUGON to test it
Michal
>
> John.
>
>> CT_ERROR(ct, "Invalid offsets head=%u tail=%u (size=%u)\n",
>> head, tail, size);
>> desc->status |= GUC_CTB_STATUS_OVERFLOW;
>> goto corrupted;
>> }
>> +#endif
>> /* tail == head condition indicates empty */
>> available = tail - head;
>> @@ -803,6 +832,7 @@ static int ct_read(struct intel_guc_ct *ct, struct
>> ct_incoming_msg **msg)
>> }
>> CT_DEBUG(ct, "received %*ph\n", 4 * len, (*msg)->msg);
>> + ctb->head = head;
>> /* now update descriptor */
>> WRITE_ONCE(desc->head, head);
>> 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 bee03794c1eb..edd1bba0445d 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>> @@ -33,6 +33,9 @@ struct intel_guc;
>> * @desc: pointer to the buffer descriptor
>> * @cmds: pointer to the commands buffer
>> * @size: size of the commands buffer in dwords
>> + * @head: local shadow copy of head in dwords
>> + * @tail: local shadow copy of tail in dwords
>> + * @space: local shadow copy of space in dwords
>> * @broken: flag to indicate if descriptor data is broken
>> */
>> struct intel_guc_ct_buffer {
>> @@ -40,6 +43,9 @@ struct intel_guc_ct_buffer {
>> struct guc_ct_buffer_desc *desc;
>> u32 *cmds;
>> u32 size;
>> + u32 tail;
>> + u32 head;
>> + u32 space;
>> bool broken;
>> };
>>
>
