From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>, olivier.matz@6wind.com
Cc: "Emil Berg" <emil.berg@ericsson.com>,
bruce.richardson@intel.com, stephen@networkplumber.org,
stable@dpdk.org, bugzilla@dpdk.org, dev@dpdk.org,
onar.olsen@ericsson.com,
"Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
Subject: RE: [PATCH 2/2] net: have checksum routines accept unaligned data
Date: Thu, 7 Jul 2022 23:44:45 +0200 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D871B1@smartserver.smartshare.dk> (raw)
In-Reply-To: <20220707183450.3203361-2-hofors@lysator.liu.se>
> From: Mattias Rönnblom [mailto:hofors@lysator.liu.se]
> Sent: Thursday, 7 July 2022 20.35
>
> From: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>
> __rte_raw_cksum() (used by rte_raw_cksum() among others) accessed its
> data through an uint16_t pointer, which allowed the compiler to assume
> the data was 16-bit aligned. This in turn would, with certain
> architectures and compiler flag combinations, result in code with SIMD
> load or store instructions with restrictions on data alignment.
>
> This patch keeps the old algorithm, but data is read using memcpy()
> instead of direct pointer access, forcing the compiler to always
> generate code that handles unaligned input. The __may_alias__ GCC
> attribute is no longer needed.
>
> The data on which the Internet checksum functions operates are almost
> always 16-bit aligned, but there are exceptions. In particular, the
> PDCP protocol header may (literally) have an odd size.
>
> Performance impact seems to range from none to a very slight
> regression.
>
> Bugzilla ID: 1035
> Cc: stable@dpdk.org
>
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---
> lib/net/rte_ip.h | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index b502481670..a9e6251f14 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -160,18 +160,23 @@ rte_ipv4_hdr_len(const struct rte_ipv4_hdr
> *ipv4_hdr)
> static inline uint32_t
> __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 void *end;
I would set "end" here instead, possibly making the pointer const too. And add spaces around '/'.
const void * const end = RTE_PTR_ADD(buf, (len / sizeof(uint16_t)) * sizeof(uint16_t));
>
> - for (; u16_buf != end; ++u16_buf)
> - sum += *u16_buf;
> + for (end = RTE_PTR_ADD(buf, (len/sizeof(uint16_t)) *
> sizeof(uint16_t));
> + 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)) {
> + uint8_t last;
> uint16_t left = 0;
> - *(unsigned char *)&left = *(const unsigned char *)end;
> +
> + memcpy(&last, end, 1);
> + *(unsigned char *)&left = last;
Couldn't you just memcpy(&left, end, 1), and omit the temporary variable "last"?
> sum += left;
> }
>
> --
> 2.25.1
>
With our without my suggested changes, it looks good.
Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
next prev parent reply other threads:[~2022-07-07 21:44 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
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 [this message]
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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