From: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
To: Olivier Matz <olivier.matz@6wind.com>
Cc: "Emil Berg" <emil.berg@ericsson.com>,
"bruce.richardson@intel.com" <bruce.richardson@intel.com>,
"stephen@networkplumber.org" <stephen@networkplumber.org>,
"stable@dpdk.org" <stable@dpdk.org>,
"bugzilla@dpdk.org" <bugzilla@dpdk.org>,
"dev@dpdk.org" <dev@dpdk.org>,
"Onar Olsen" <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 10:53:27 +0000 [thread overview]
Message-ID: <466bcfdd-3eb0-839c-0689-52c2e269d195@ericsson.com> (raw)
In-Reply-To: <YsvzAsy8gG4ArPq7@platinum>
On 2022-07-11 11:53, Olivier Matz wrote:
> 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 '/' :)
>
Shorter, more readable. Looks good to me.
Thanks.
>
>> + 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
>>
next prev parent reply other threads:[~2022-07-11 10:53 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
2022-07-11 10:53 ` Mattias Rönnblom [this message]
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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