On Mon, May 24, 2021 at 03:43:11PM +0200, Michal Wajdeczko wrote: > > > On 06.05.2021 21:13, 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@xxxxxxxxx> > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > > --- > > 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 77dfbc94dcc3..d6895d29ed2d 100644 > > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c > > @@ -63,11 +63,16 @@ 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 > > + * 16 bytes which gives us a maximum 256 queue'd requests. Hopefully this > > nit: all our CTB calculations are in dwords now, not bytes > I can change the wording to DW sizes. > > + * 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. > > hmm, but we are not checking G2H CTB yet > will start doing it around patch 54/97 > so maybe this other patch should be introduced earlier ? > Yes, that patch is going to be pulled down to an earlier spot in the series. > > */ > > #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) > > in theory, we (host) should be faster than GuC, so G2H CTB shall be > almost always empty, if this is not a case, maybe we should start > monitoring what is happening and report some warnings if G2H is half full ? > Certainly some IGTs put some more pressure on the G2H channel than the H2G channel at least I think. This is something we can tune over time after this lands upstream. IMO a message at this point is overkill. Matt > > > > #define MAX_US_STALL_CTB 1000000 > > > > @@ -753,7 +758,7 @@ 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); > > GEM_BUG_ON(available < 0); > > > > header = cmds[head]; > >
