Re: [PATCH 03/24] checksum: align buffers

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 5 Feb 2024 17:02:00 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, Feb 02, 2024 at 03:11:30PM +0100, Laurent Vivier wrote:
> > if buffer is not aligned use sum_16b() only on the not aligned
> > part, and then use csum() on the remaining part
> > 
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>  
> 
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> 
> > ---
> >  checksum.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/checksum.c b/checksum.c
> > index f21c9b7a14d1..c94980771c63 100644
> > --- a/checksum.c
> > +++ b/checksum.c
> > @@ -407,7 +407,19 @@ less_than_128_bytes:
> >  __attribute__((optimize("-fno-strict-aliasing")))	/* See csum_16b() */
> >  uint16_t csum(const void *buf, size_t len, uint32_t init)
> >  {
> > -	return (uint16_t)~csum_fold(csum_avx2(buf, len, init));
> > +	intptr_t align = ((intptr_t)buf + 0x1f) & ~(intptr_t)0x1f;  
> 
> Wonder if its worth adding an ALIGN_UP macro.

Actually, we have it, it's called ROUND_UP (see util.h). This could be:

	intptr_t align = ROUND_UP(buf, 0x20);

...and maybe we could use sizeof(__m256i) or similar instead of 0x20.

> 
> > +	unsigned int pad = align - (intptr_t)buf;
> > +
> > +	if (len < pad)
> > +		pad = len;
> > +
> > +	if (pad)
> > +		init += sum_16b(buf, pad);
> > +
> > +	if (len > pad)
> > +		init = csum_avx2((void *)align, len - pad, init);
> > +
> > +	return (uint16_t)~csum_fold(init);
> >  }
> >  
> >  #else /* __AVX2__ */  
> 

-- 
Stefano