[dpdk-dev] [PATCH 1/2] net/mlx5: remove redundant operations

[Slava Ovsiienko]

Hi, Ruifeng

The invalid_mask is used to set error flags and calculate the statistics.
So, all the CQEs the first one with error or invalid status should be masked out
(and the CQEs after that).

IMO, what we could improve (apply just the part of the patch below):
>>>>
index 2234fbe6b2..98a75b09c6 100644
--- a/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
+++ b/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
@@ -768,18 +768,11 @@  rxq_cq_process_v(struct mlx5_rxq_data *rxq, volatile struct mlx5_cqe *cq,
 					  comp_mask), 0)) /
 					  (sizeof(uint16_t) * 8);
 		/* D.6 mask out entries after the compressed CQE. */
-		mask = vcreate_u16(comp_idx < MLX5_VPMD_DESCS_PER_LOOP ?
-				   -1UL >> (comp_idx * sizeof(uint16_t) * 8) :
-				   0);
-		invalid_mask = vorr_u16(invalid_mask, mask);
+		invalid_mask = vorr_u16(invalid_mask, comp_mask);
 		/* D.7 count non-compressed valid CQEs. */
 		n = __builtin_clzl(vget_lane_u64(vreinterpret_u64_u16(
 				   invalid_mask), 0)) / (sizeof(uint16_t) * 8);
 		nocmp_n += n;
<<<<

And that's it. The rest of the patch:
>>>>
-		/* D.2 get the final invalid mask. */
-		mask = vcreate_u16(n < MLX5_VPMD_DESCS_PER_LOOP ?
-				   -1UL >> (n * sizeof(uint16_t) * 8) : 0);
-		invalid_mask = vorr_u16(invalid_mask, mask);
<<<<
Should not be applied, otherwise the following might be affected:

opcode = vbic_u16(opcode, invalid_mask);
...
opcode = vbic_u16(opcode, invalid_mask);

With best regards,
Slava

> -----Original Message-----
> From: Ruifeng Wang <Ruifeng.Wang at arm.com>
> Sent: Friday, July 2, 2021 13:30
> To: Slava Ovsiienko <viacheslavo at nvidia.com>; Raslan Darawsheh
> <rasland at nvidia.com>; Matan Azrad <matan at nvidia.com>; Shahaf Shuler
> <shahafs at nvidia.com>
> Cc: dev at dpdk.org; jerinj at marvell.com; nd <nd at arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli at arm.com>; stable at dpdk.org; nd
> <nd at arm.com>
> Subject: RE: [PATCH 1/2] net/mlx5: remove redundant operations
> 
> > -----Original Message-----
> > From: Slava Ovsiienko <viacheslavo at nvidia.com>
> > Sent: Friday, July 2, 2021 4:13 PM
> > To: Ruifeng Wang <Ruifeng.Wang at arm.com>; Raslan Darawsheh
> > <rasland at nvidia.com>; Matan Azrad <matan at nvidia.com>; Shahaf Shuler
> > <shahafs at nvidia.com>
> > Cc: dev at dpdk.org; jerinj at marvell.com; nd <nd at arm.com>; Honnappa
> > Nagarahalli <Honnappa.Nagarahalli at arm.com>; stable at dpdk.org
> > Subject: RE: [PATCH 1/2] net/mlx5: remove redundant operations
> >
> > Hi, Ruifeng
> Hi, Slava
> 
> >
> > > -----Original Message-----
> > > From: Ruifeng Wang <ruifeng.wang at arm.com>
> > > Sent: Tuesday, June 1, 2021 11:31
> > > To: Raslan Darawsheh <rasland at nvidia.com>; Matan Azrad
> > > <matan at nvidia.com>; Shahaf Shuler <shahafs at nvidia.com>; Slava
> > > Ovsiienko <viacheslavo at nvidia.com>
> > > Cc: dev at dpdk.org; jerinj at marvell.com; nd at arm.com;
> > > honnappa.nagarahalli at arm.com; Ruifeng Wang
> <ruifeng.wang at arm.com>;
> > > stable at dpdk.org
> > > Subject: [PATCH 1/2] net/mlx5: remove redundant operations
> > >
> > > Some operations on mask are redundant and can be removed.
> > > The change yielded 1.6% performance gain on N1SDP.
> > > On ThunderX2, slight performance uplift was also observed.
> > >
> > > Fixes: 570acdb1da8a ("net/mlx5: add vectorized Rx/Tx burst for ARM")
> > > Cc: stable at dpdk.org
> > >
> > > Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > > ---
> > >  drivers/net/mlx5/mlx5_rxtx_vec_neon.h | 9 +--------
> > >  1 file changed, 1 insertion(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
> > > b/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
> > > index 2234fbe6b2..98a75b09c6 100644
> > > --- a/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
> > > +++ b/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
> > > @@ -768,18 +768,11 @@ rxq_cq_process_v(struct mlx5_rxq_data *rxq,
> > > volatile struct mlx5_cqe *cq,
> > >  					  comp_mask), 0)) /
> > >  					  (sizeof(uint16_t) * 8);
> > >  		/* D.6 mask out entries after the compressed CQE. */
> > > -		mask = vcreate_u16(comp_idx <
> > > MLX5_VPMD_DESCS_PER_LOOP ?
> > > -				   -1UL >> (comp_idx * sizeof(uint16_t) * 8) :
> > > -				   0);
> > > -		invalid_mask = vorr_u16(invalid_mask, mask);
> > > +		invalid_mask = vorr_u16(invalid_mask, comp_mask);
> >
> > Mmmm... I'm not sure we can drop the masking compressed (and
> > following) CQE skip.
> > Let's consider the completion scenario (the series of 4 CQEs, each
> > element is 64B long)
> >
> > 0: normal uncompressed CQE, ownership OK, format uncompressed, opcode
> > OK, no error
> > 1: compressed CQE, ownership OK, format compressed, opcode OK, no
> > error
> > 2: miniCQE array, format can be any!!, may be discovered as ownership
> > OK, format uncompressed, opcode OK, no error
> > 3: miniCQE array, format can be any!!, may be discovered as ownership
> > OK, format uncompressed, opcode OK, no error
> 
> Thanks for your review and explanation about CQE processing details.
> I did the change based on the fact that some calculations doesn't change the
> data.
> So some intermediate calculations were removed.
> 
> In the above diff section, result of 'mask' always equals to the nearest
> 'comp_mask' that above it.
> So I just remoed 'mask' and use 'comp_mask' instead.
> >
> > Obviously, we should unconditionally mask out 2 and 3, regardless of
> > recognized their formats/opcode/error/etc.
> > I think we can get the diff above and skip diff below:
> >
> > >  		/* D.7 count non-compressed valid CQEs. */
> > >  		n = __builtin_clzl(vget_lane_u64(vreinterpret_u64_u16(
> > >  				   invalid_mask), 0)) / (sizeof(uint16_t) * 8);
> > >  		nocmp_n += n;
> > > -		/* D.2 get the final invalid mask. */
> > > -		mask = vcreate_u16(n < MLX5_VPMD_DESCS_PER_LOOP ?
> > > -				   -1UL >> (n * sizeof(uint16_t) * 8) : 0);
> > > -		invalid_mask = vorr_u16(invalid_mask, mask);
> >
> > and get the correct final invalid_mask - all compressed and invalid
> > CQEs and following ones will be masked out.
> 
> This diff section is similar to the previous one.
> 'mask' always equals to the nearest 'invalid_mask' that above it.
> So entire line "invalid_mask = vorr_u16(invalid_mask, mask);" can be removed.
> 
> Code logic is not changed. But I'm not sure the code change impacts readability
> or maintainability that you may concern.
> 
> Thanks.
> >
> > With best regards,
> > Slava