RE: [PATCH v4] net: fix checksum with unaligned buffer

[Emil Berg <emil.berg@ericsson.com>]

> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: den 23 juni 2022 14:51
> To: Emil Berg <emil.berg@ericsson.com>; bruce.richardson@intel.com;
> dev@dpdk.org
> Cc: stephen@networkplumber.org; stable@dpdk.org; bugzilla@dpdk.org;
> hofors@lysator.liu.se; olivier.matz@6wind.com
> Subject: RE: [PATCH v4] net: fix checksum with unaligned buffer
> 
> > From: Morten Brørup [mailto:mb@smartsharesystems.com]
> > Sent: Thursday, 23 June 2022 14.39
> >
> > With this patch, the checksum can be calculated on an unaligned buffer.
> > I.e. the buf parameter is no longer required to be 16 bit aligned.
> >
> > The checksum is still calculated using a 16 bit aligned pointer, so
> > the compiler can auto-vectorize the function's inner loop.
> >
> > When the buffer is unaligned, the first byte of the buffer is handled
> > separately. Furthermore, the calculated checksum of the buffer is byte
> > shifted before being added to the initial checksum, to compensate for
> > the checksum having been calculated on the buffer shifted by one byte.
> >
> > v4:
> > * Add copyright notice.
> > * Include stdbool.h (Emil Berg).
> > * Use RTE_PTR_ADD (Emil Berg).
> > * Fix one more typo in commit message. Is 'unligned' even a word?
> > v3:
> > * Remove braces from single statement block.
> > * Fix typo in commit message.
> > v2:
> > * Do not assume that the buffer is part of an aligned packet buffer.
> >
> > Bugzilla ID: 1035
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> > Tested-by: Emil Berg <emil.berg@ericsson.com>
> > ---
> >  lib/net/rte_ip.h | 32 +++++++++++++++++++++++++++-----
> >  1 file changed, 27 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h index
> > b502481670..738d643da0 100644
> > --- a/lib/net/rte_ip.h
> > +++ b/lib/net/rte_ip.h
> > @@ -3,6 +3,7 @@
> >   *      The Regents of the University of California.
> >   * Copyright(c) 2010-2014 Intel Corporation.
> >   * Copyright(c) 2014 6WIND S.A.
> > + * Copyright(c) 2022 SmartShare Systems.
> >   * All rights reserved.
> >   */
> >
> > @@ -15,6 +16,7 @@
> >   * IP-related defines
> >   */
> >
> > +#include <stdbool.h>
> >  #include <stdint.h>
> >
> >  #ifdef RTE_EXEC_ENV_WINDOWS
> > @@ -162,20 +164,40 @@ __rte_raw_cksum(const void *buf, size_t len,
> > uint32_t sum)  {
> >  	/* extend strict-aliasing rules */
> >  	typedef uint16_t __attribute__((__may_alias__)) u16_p;
> > -	const u16_p *u16_buf = (const u16_p *)buf;
> > -	const u16_p *end = u16_buf + len / sizeof(*u16_buf);
> > +	const u16_p *u16_buf;
> > +	const u16_p *end;
> > +	uint32_t bsum = 0;
> > +	const bool unaligned = (uintptr_t)buf & 1;
> > +
> > +	/* if buffer is unaligned, keeping it byte order independent */
> > +	if (unlikely(unaligned)) {
> > +		uint16_t first = 0;
> > +		if (unlikely(len == 0))
> > +			return 0;
> > +		((unsigned char *)&first)[1] = *(const unsigned
> char *)buf;
> > +		bsum += first;
> > +		buf = RTE_PTR_ADD(buf, 1);
> > +		len--;
> > +	}
> >
> > +	/* aligned access for compiler auto-vectorization */
> > +	u16_buf = (const u16_p *)buf;
> > +	end = u16_buf + len / sizeof(*u16_buf);
> >  	for (; u16_buf != end; ++u16_buf)
> > -		sum += *u16_buf;
> > +		bsum += *u16_buf;
> >
> >  	/* if length is odd, keeping it byte order independent */
> >  	if (unlikely(len % 2)) {
> >  		uint16_t left = 0;
> >  		*(unsigned char *)&left = *(const unsigned char
> *)end;
> > -		sum += left;
> > +		bsum += left;
> >  	}
> >
> > -	return sum;
> > +	/* if buffer is unaligned, swap the checksum bytes */
> > +	if (unlikely(unaligned))
> > +		bsum = (bsum & 0xFF00FF00) >> 8 | (bsum &
> 0x00FF00FF) << 8;
> > +
> > +	return sum + bsum;
> >  }
> >
> >  /**
> > --
> > 2.17.1
> 
> @Emil, thank you for thoroughly reviewing the previous versions.
> 
> If your test succeeds and you are satisfied with the patch, remember to reply
> with a "Tested-by" tag for patchwork.

The test succeeded and I'm satisfied with the patch. I added 'Tested-by: Emil Berg <emil.berg@ericsson.com>' to the patch above, hopefully as you intended.