Re: [PATCH 03/47] drm/i915/guc: Increase size of CTB buffers

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 24.06.2021 17:41, Matthew Brost wrote:
> On Thu, Jun 24, 2021 at 03:49:55PM +0200, Michal Wajdeczko wrote:
>>
>>
>> On 24.06.2021 09:04, Matthew Brost wrote:
>>> With the introduction of non-blocking CTBs more than one CTB can be in
>>> flight at a time. Increasing the size of the CTBs should reduce how
>>> often software hits the case where no space is available in the CTB
>>> buffer.
>>>
>>> Cc: John Harrison <john.c.harrison@intel.com>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 11 ++++++++---
>>>  1 file changed, 8 insertions(+), 3 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 07f080ddb9ae..a17215920e58 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> @@ -58,11 +58,16 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
>>>   *      +--------+-----------------------------------------------+------+
>>>   *
>>>   * Size of each `CT Buffer`_ must be multiple of 4K.
>>> - * As we don't expect too many messages, for now use minimum sizes.
>>> + * We don't expect too many messages in flight at any time, unless we are
>>> + * using the GuC submission. In that case each request requires a minimum
>>> + * 2 dwords which gives us a maximum 256 queue'd requests. Hopefully this
>>> + * enough space to avoid backpressure on the driver. We increase the size
>>> + * of the receive buffer (relative to the send) to ensure a G2H response
>>> + * CTB has a landing spot.
>>>   */
>>>  #define CTB_DESC_SIZE		ALIGN(sizeof(struct guc_ct_buffer_desc), SZ_2K)
>>>  #define CTB_H2G_BUFFER_SIZE	(SZ_4K)
>>> -#define CTB_G2H_BUFFER_SIZE	(SZ_4K)
>>> +#define CTB_G2H_BUFFER_SIZE	(4 * CTB_H2G_BUFFER_SIZE)
>>>  
>>>  struct ct_request {
>>>  	struct list_head link;
>>> @@ -641,7 +646,7 @@ static int ct_read(struct intel_guc_ct *ct, struct ct_incoming_msg **msg)
>>>  	/* beware of buffer wrap case */
>>>  	if (unlikely(available < 0))
>>>  		available += size;
>>> -	CT_DEBUG(ct, "available %d (%u:%u)\n", available, head, tail);
>>> +	CT_DEBUG(ct, "available %d (%u:%u:%u)\n", available, head, tail, size);
>>
>> CTB size is already printed in intel_guc_ct_init() and is fixed so not
>> sure if repeating it on every ct_read has any benefit
>>
> 
> I'd say more debug the better and if CT_DEBUG is enabled the logs are
> very verbose so an extra value doesn't really hurt.

fair, but this doesn't mean we should add little/no value item, anyway
since DEBUG_GUC is if off by default, this is:

Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>

> 
> Matt
> 
>>>  	GEM_BUG_ON(available < 0);
>>>  
>>>  	header = cmds[head];
>>>