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

Saleem, Shiraz
2023-04-12T17:04:27Z

> 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@wanadoo.fr>
> > ---
> > 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@intel.com>