RE: [PATCH] RDMA/irdma: Slightly optimize irdma_form_ah_cm_frame()

[Saleem, Shiraz]

> Subject: Re: [PATCH] RDMA/irdma: Slightly optimize
> irdma_form_ah_cm_frame()
> 
> On Thu, Feb 02, 2023 at 09:23:24PM +0100, Christophe JAILLET wrote:
> > There is no need to zero 'pktsize' bytes of 'buf', only the header
> > needs to be cleared, to be safe.
> > All the other bytes are already written with some memcpy() at the end
> > of the function.
> >
> > Doing so also gives the opportunity to the compiler to avoid the
> > memset() call. It can be inlined now that the length is known as compile time.
> >
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> > Just in case, here is the diff of what is generated by gcc 11.3.0
> > before and after the patch.
> >
> >  .L736:
> > -# drivers/infiniband/hw/irdma/cm.c:340: 	memset(buf, 0, pktsize);
> > +# drivers/infiniband/hw/irdma/cm.c:340: 	memset(buf, 0, sizeof(*tcph));
> >  	call	__sanitizer_cov_trace_pc	#
> > -	xorl	%esi, %esi	#
> > -	movzwl	%r13w, %edx	# _194, __fortify_size
> > -	movq	%rbp, %rdi	# buf,
> > -	call	memset	#
> > -	leaq	104(%r12), %rax	#, _259
> > +	movl	$0, 16(%rbp)	#, MEM <char[1:20]> [(void *)buf_114]
> > +	leaq	104(%r12), %rax	#, _295
> > +# drivers/infiniband/hw/irdma/cm.c:342: 	sqbuf->totallen = pktsize;
> > +	movzwl	%r13w, %r13d	# _192, _192
> > +# drivers/infiniband/hw/irdma/cm.c:340: 	memset(buf, 0, sizeof(*tcph));
> > +	movq	$0, 0(%rbp)	#, MEM <char[1:20]> [(void *)buf_114]
> > +# drivers/infiniband/hw/irdma/cm.c:342: 	sqbuf->totallen = pktsize;
> > +	movq	%rax, %rdi	# _295,
> > +# drivers/infiniband/hw/irdma/cm.c:340: 	memset(buf, 0, sizeof(*tcph));
> > +	movq	$0, 8(%rbp)	#, MEM <char[1:20]> [(void *)buf_114]
> > +	movq	%rax, 64(%rsp)	# _295, %sfp
> >  # drivers/infiniband/hw/irdma/cm.c:342: 	sqbuf->totallen = pktsize;
> > ---
> >  drivers/infiniband/hw/irdma/cm.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Shiraz??
> 

Sorry for the delay as I didn't see this earlier.

Reviewed-by: Shiraz Saleem <shiraz.saleem@xxxxxxxxx>