From: Emil Berg <emil.berg@ericsson.com>
To: "Morten Brørup" <mb@smartsharesystems.com>
Cc: "stable@dpdk.org" <stable@dpdk.org>,
"bugzilla@dpdk.org" <bugzilla@dpdk.org>,
"hofors@lysator.liu.se" <hofors@lysator.liu.se>,
"olivier.matz@6wind.com" <olivier.matz@6wind.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: RE: [PATCH] net: fix checksum with unaligned buffer
Date: Mon, 20 Jun 2022 10:37:41 +0000 [thread overview]
Message-ID: <AM8PR07MB766628919D85FADCE736DD1E98B09@AM8PR07MB7666.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D8713A@smartserver.smartshare.dk>
> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: den 17 juni 2022 11:07
> To: Emil Berg <emil.berg@ericsson.com>
> Cc: stable@dpdk.org; bugzilla@dpdk.org; hofors@lysator.liu.se;
> olivier.matz@6wind.com; dev@dpdk.org
> Subject: RE: [PATCH] net: fix checksum with unaligned buffer
>
> > From: Morten Brørup [mailto:mb@smartsharesystems.com]
> > Sent: Friday, 17 June 2022 10.45
> >
> > With this patch, the checksum can be calculated on an unligned part of
> > a packet buffer.
> > I.e. the buf parameter is no longer required to be 16 bit aligned.
> >
> > The DPDK invariant that packet buffers must be 16 bit aligned remains
> > unchanged.
> > This invariant also defines how to calculate the 16 bit checksum on an
> > unaligned part of a packet buffer.
> >
> > Bugzilla ID: 1035
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> > ---
> > lib/net/rte_ip.h | 17 +++++++++++++++--
> > 1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h index
> > b502481670..8e301d9c26 100644
> > --- a/lib/net/rte_ip.h
> > +++ b/lib/net/rte_ip.h
> > @@ -162,9 +162,22 @@ __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;
> > +
> > + /* if buffer is unaligned, keeping it byte order independent */
> > + if (unlikely((uintptr_t)buf & 1)) {
> > + uint16_t first = 0;
> > + if (unlikely(len == 0))
> > + return 0;
> > + ((unsigned char *)&first)[1] = *(const unsigned
> char *)buf;
> > + sum += first;
> > + buf = (const void *)((uintptr_t)buf + 1);
> > + len--;
> > + }
> >
> > + u16_buf = (const u16_p *)buf;
> > + end = u16_buf + len / sizeof(*u16_buf);
> > for (; u16_buf != end; ++u16_buf)
> > sum += *u16_buf;
> >
> > --
> > 2.17.1
>
> @Emil, can you please test this patch with an unaligned buffer on your
> application to confirm that it produces the expected result.
Hi!
I tested the patch. It doesn't seem to produce the same results. I think the problem is that it always starts summing from an even address, the sum should always start from the first byte according to the checksum specification. Can I instead propose something Mattias Rönnblom sent me?
--------------------------------------------------------------------------------------------------------------
const void *end = RTE_PTR_ADD(buf, (len / sizeof(uint16_t)) * sizeof(uint16_t));
for (; buf != end; buf = RTE_PTR_ADD(buf, sizeof(uint16_t))) {
uint16_t v;
memcpy(&v, buf, sizeof(uint16_t));
sum += v;
}
/* 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;
}
--------------------------------------------------------------------------------------------------------------
Note that the last block is the same as before. Amazingly I see no measurable performance hit from this compared to the previous one (-O3, march=native). Looking at the previous the loop body may compile to (x86):
--------------------------------------------------------------------------------------------------------------
vmovdqa (%rdx),%xmm1
vpmovzxwd %xmm1,%xmm0
vpsrldq $0x8,%xmm1,%xmm1
vpmovzxwd %xmm1,%xmm1
vpaddd %xmm1,%xmm0,%xmm0
cmp $0xf,%rax
jbe 0x7ff7a0dfb1a9
--------------------------------------------------------------------------------------------------------------
while Mattias' memcpy solution:
--------------------------------------------------------------------------------------------------------------
vmovdqu (%rcx),%ymm0
add $0x20,%rcx
vpmovzxwd %xmm0,%ymm1
vextracti128 $0x1,%ymm0,%xmm0
vpmovzxwd %xmm0,%ymm0
vpaddd %ymm0,%ymm1,%ymm0
vpaddd %ymm0,%ymm2,%ymm2
cmp %r9,%rcx
jne 0x555555556380
--------------------------------------------------------------------------------------------------------------
Thus two extra instructions in the loop, but I suspect it may be memory bound, leading to no measurable performance difference.
Any comments?
/Emil
next prev parent reply other threads:[~2022-06-22 6:01 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 7:16 [Bug 1035] __rte_raw_cksum() crash with misaligned pointer bugzilla
2022-06-15 14:40 ` Morten Brørup
2022-06-16 5:44 ` Emil Berg
2022-06-16 6:27 ` Morten Brørup
2022-06-16 6:32 ` Emil Berg
2022-06-16 6:44 ` Morten Brørup
2022-06-16 13:58 ` Mattias Rönnblom
2022-06-16 14:36 ` Morten Brørup
2022-06-17 7:32 ` Morten Brørup
2022-06-17 8:45 ` [PATCH] net: fix checksum with unaligned buffer Morten Brørup
2022-06-17 9:06 ` Morten Brørup
2022-06-17 12:17 ` Emil Berg
2022-06-20 10:37 ` Emil Berg [this message]
2022-06-20 10:57 ` Morten Brørup
2022-06-21 7:16 ` Emil Berg
2022-06-21 8:05 ` Morten Brørup
2022-06-21 8:23 ` Bruce Richardson
2022-06-21 9:35 ` Morten Brørup
2022-06-22 6:26 ` Emil Berg
2022-06-22 9:18 ` Bruce Richardson
2022-06-22 11:26 ` Morten Brørup
2022-06-22 12:25 ` Emil Berg
2022-06-22 14:01 ` Morten Brørup
2022-06-22 14:03 ` Emil Berg
2022-06-23 5:21 ` Emil Berg
2022-06-23 7:01 ` Morten Brørup
2022-06-23 11:39 ` Emil Berg
2022-06-23 12:18 ` Morten Brørup
2022-06-22 13:44 ` [PATCH v2] " Morten Brørup
2022-06-22 13:54 ` [PATCH v3] " Morten Brørup
2022-06-23 12:39 ` [PATCH v4] " Morten Brørup
2022-06-23 12:51 ` Morten Brørup
2022-06-27 7:56 ` Emil Berg
2022-06-27 10:54 ` Morten Brørup
2022-06-27 12:28 ` Mattias Rönnblom
2022-06-27 12:46 ` Emil Berg
2022-06-27 12:50 ` Emil Berg
2022-06-27 13:22 ` Morten Brørup
2022-06-27 17:22 ` Mattias Rönnblom
2022-06-27 20:21 ` Morten Brørup
2022-06-28 6:28 ` Mattias Rönnblom
2022-06-30 16:28 ` Morten Brørup
2022-07-07 15:21 ` Stanisław Kardach
2022-07-07 18:34 ` [PATCH 1/2] app/test: add cksum performance test Mattias Rönnblom
2022-07-07 18:34 ` [PATCH 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-07 21:44 ` Morten Brørup
2022-07-08 12:43 ` Mattias Rönnblom
2022-07-08 12:56 ` [PATCH v2 1/2] app/test: add cksum performance test Mattias Rönnblom
2022-07-08 12:56 ` [PATCH v2 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-08 14:44 ` Ferruh Yigit
2022-07-11 9:53 ` Olivier Matz
2022-07-11 10:53 ` Mattias Rönnblom
2022-07-11 9:47 ` [PATCH v2 1/2] app/test: add cksum performance test Olivier Matz
2022-07-11 10:42 ` Mattias Rönnblom
2022-07-11 11:33 ` Olivier Matz
2022-07-11 12:11 ` [PATCH v3 " Mattias Rönnblom
2022-07-11 12:11 ` [PATCH v3 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-11 13:25 ` Olivier Matz
2022-08-08 9:25 ` Mattias Rönnblom
2022-09-20 12:09 ` Mattias Rönnblom
2022-09-20 16:10 ` Thomas Monjalon
2022-07-11 13:20 ` [PATCH v3 1/2] app/test: add cksum performance test Olivier Matz
2022-07-08 13:02 ` [PATCH 2/2] net: have checksum routines accept unaligned data Morten Brørup
2022-07-08 13:52 ` Mattias Rönnblom
2022-07-08 14:10 ` Bruce Richardson
2022-07-08 14:30 ` Morten Brørup
2022-06-30 17:41 ` [PATCH v4] net: fix checksum with unaligned buffer Stephen Hemminger
2022-06-30 17:45 ` Stephen Hemminger
2022-07-01 4:11 ` Emil Berg
2022-07-01 16:50 ` Morten Brørup
2022-07-01 17:04 ` Stephen Hemminger
2022-07-01 20:46 ` Morten Brørup
2022-06-16 14:09 ` [Bug 1035] __rte_raw_cksum() crash with misaligned pointer Mattias Rönnblom
2022-10-10 10:40 ` bugzilla
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