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

[Matthew Brost <matthew.brost@intel.com>]

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.

Matt

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