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From: Olivier Matz <olivier.matz@6wind.com>
To: "Mattias Rönnblom" <mattias.ronnblom@ericsson.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,
	"Morten Brørup" <mb@smartsharesystems.com>
Subject: Re: [PATCH v2 2/2] net: have checksum routines accept unaligned data
Date: Mon, 11 Jul 2022 11:53:06 +0200	[thread overview]
Message-ID: <YsvzAsy8gG4ArPq7@platinum> (raw)
In-Reply-To: <20220708125608.24532-2-mattias.ronnblom@ericsson.com>

Hi,

On Fri, Jul 08, 2022 at 02:56:08PM +0200, Mattias Rönnblom wrote:
> __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
> 
> ---

Using memcpy() looks to be a good solution fix the issue, while avoiding a
branch and the __may_alias__.

I just have one minor comment below.

> 
> v2:
>   * Simplified the odd-length conditional (Morten Brørup).
> 
> Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
> 
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---
>  lib/net/rte_ip.h | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index b502481670..a0334d931e 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -160,18 +160,21 @@ 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;
>  
> -	for (; u16_buf != end; ++u16_buf)
> -		sum += *u16_buf;
> +	for (end = RTE_PTR_ADD(buf, (len/sizeof(uint16_t)) * sizeof(uint16_t));

What do you think about this form:

	for (end = RTE_PTR_ADD(buf, RTE_ALIGN_FLOOR(len, sizeof(uint16_t)));

This also has the good property to solve the debate about the
spaces around the '/' :)


> +	     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;
> +
> +		memcpy(&left, end, 1);
>  		sum += left;
>  	}
>  
> -- 
> 2.25.1
> 

  parent reply	other threads:[~2022-07-11  9:53 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
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 [this message]
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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