From: "Mattias Rönnblom" <hofors@lysator.liu.se>
To: "Morten Brørup" <mb@smartsharesystems.com>,
"Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
dev@dpdk.org, "Tyler Retzlaff" <roretzla@linux.microsoft.com>
Cc: Heng Wang <heng.wang@ericsson.com>,
Stephen Hemminger <stephen@networkplumber.org>,
techboard@dpdk.org
Subject: Re: [RFC v2 5/6] eal: add atomic bit operations
Date: Fri, 26 Apr 2024 11:39:17 +0200 [thread overview]
Message-ID: <7e469926-0c09-42a4-aa8f-8cde0578690b@lysator.liu.se> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F3EF@smartserver.smartshare.dk>
On 2024-04-25 18:18, Morten Brørup wrote:
>> From: Mattias Rönnblom [mailto:hofors@lysator.liu.se]
>> Sent: Thursday, 25 April 2024 16.36
>>
>> On 2024-04-25 12:25, Morten Brørup wrote:
>>>> +#define rte_bit_atomic_test(addr, nr, memory_order)
>> \
>>>> + _Generic((addr), \
>>>> + uint32_t *: __rte_bit_atomic_test32, \
>>>> + uint64_t *: __rte_bit_atomic_test64)(addr, nr,
>> memory_order)
>>>
>>> I wonder if these should have RTE_ATOMIC qualifier:
>>>
>>> + RTE_ATOMIC(uint32_t) *: __rte_bit_atomic_test32,
>> \
>>> + RTE_ATOMIC(uint64_t) *: __rte_bit_atomic_test64)(addr, nr,
>> memory_order)
>>>
>>>
>>>> +#define __RTE_GEN_BIT_ATOMIC_TEST(size)
>> \
>>>> + static inline bool \
>>>> + __rte_bit_atomic_test ## size(const uint ## size ## _t *addr,
>> \
>>>
>>> I wonder if the "addr" parameter should have RTE_ATOMIC qualifier:
>>>
>>> + __rte_bit_atomic_test ## size(const RTE_ATOMIC(uint ## size ## _t)
>> *addr, \
>>>
>>> instead of casting into a_addr.
>>>
>>
>> Check the cover letter for the rationale for the cast.
>
> Thanks, that clarifies it. Then...
> For the series:
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
>
>>
>> Where I'm at now is that I think C11 _Atomic is rather poor design. The
>> assumption that an object which allows for atomic access always should
>> require all operations upon it to be atomic, regardless of where it is
>> in its lifetime, and which thread is accessing it, does not hold, in the
>> general case.
>
> It might be slow, but I suppose the C11 standard prioritizes correctness over performance.
>
That's a false dichotomy, in this case. You can have both.
> It seems locks are automatically added to _Atomic types larger than what is natively supported by the architecture.
> E.g. MSVC adds locks to _Atomic types larger than 8 byte. [1]
>
> [1]: https://devblogs.microsoft.com/cppblog/c11-atomics-in-visual-studio-2022-version-17-5-preview-2/
>
>>
>> The only reason for _Atomic being as it is, as far as I can see, is to
>> accommodate for ISAs which does not have the appropriate atomic machine
>> instructions, and thus require a lock or some other data associated with
>> the actual user-data-carrying bits. Neither GCC nor DPDK supports any
>> such ISAs, to my knowledge. I suspect neither never will. So the cast
>> will continue to work.
>
> I tend to agree with you on this.
>
> We should officially decide that DPDK treats RTE_ATOMIC types as a union of _Atomic and non-atomic, i.e. operations on RTE_ATOMIC types can be both atomic and non-atomic.
>
I think this is a subject which needs to be further explored.
Objects that can be accessed both atomically and non-atomically should
be without _Atomic. With my current understanding of this issue, that
seems like the best option.
You could turn it around as well, and have such marked _Atomic and have
explicit casts to their non-_Atomic cousins when operated upon by
non-atomic functions. Not sure how realistic that is, since
non-atomicity is the norm. All generic selection-based "functions" must
take this into account.
>>
>>>> + unsigned int nr, int memory_order) \
>>>> + { \
>>>> + RTE_ASSERT(nr < size); \
>>>> + \
>>>> + const RTE_ATOMIC(uint ## size ## _t) *a_addr = \
>>>> + (const RTE_ATOMIC(uint ## size ## _t) *)addr; \
>>>> + uint ## size ## _t mask = (uint ## size ## _t)1 << nr; \
>>>> + return rte_atomic_load_explicit(a_addr, memory_order) &
>> mask; \
>>>> + }
>>>
>>>
>>> Similar considerations regarding volatile qualifier for the "once"
>> operations.
>>>
next prev parent reply other threads:[~2024-04-26 9:39 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-02 13:53 [RFC 0/7] Improve EAL bit operations API Mattias Rönnblom
2024-03-02 13:53 ` [RFC 1/7] eal: extend bit manipulation functions Mattias Rönnblom
2024-03-02 17:05 ` Stephen Hemminger
2024-03-03 6:26 ` Mattias Rönnblom
2024-03-04 16:34 ` Tyler Retzlaff
2024-03-05 18:01 ` Mattias Rönnblom
2024-03-05 18:06 ` Tyler Retzlaff
2024-04-25 8:58 ` [RFC v2 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-04-25 8:58 ` [RFC v2 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-04-29 11:12 ` Morten Brørup
2024-04-30 9:55 ` [RFC v4 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 0/6] Improve EAL bit operations API Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 1/6] eal: extend bit manipulation functionality Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-05-07 19:17 ` Morten Brørup
2024-05-08 6:47 ` Mattias Rönnblom
2024-05-08 7:33 ` Morten Brørup
2024-05-08 8:00 ` Mattias Rönnblom
2024-05-08 8:11 ` Morten Brørup
2024-05-08 9:27 ` Mattias Rönnblom
2024-05-08 10:08 ` Morten Brørup
2024-05-08 15:15 ` Stephen Hemminger
2024-05-08 16:16 ` Morten Brørup
2024-05-05 8:37 ` [RFC v7 4/6] eal: add unit tests for " Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-05-05 8:37 ` [RFC v7 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 4/6] eal: add unit tests for " Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-05-03 6:41 ` Mattias Rönnblom
2024-05-03 23:30 ` Tyler Retzlaff
2024-05-04 15:36 ` Mattias Rönnblom
2024-05-02 5:57 ` [RFC v6 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 4/6] eal: add unit tests for " Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-04-30 12:08 ` [RFC v5 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 4/6] eal: add unit tests for " Mattias Rönnblom
2024-04-30 10:37 ` Morten Brørup
2024-04-30 11:58 ` Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-04-30 9:55 ` [RFC v4 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 4/6] eal: add unit tests for " Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-04-29 9:51 ` [RFC v3 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-04-25 8:58 ` [RFC v2 2/6] eal: add unit tests for bit operations Mattias Rönnblom
2024-04-25 8:58 ` [RFC v2 3/6] eal: add exactly-once bit access functions Mattias Rönnblom
2024-04-25 8:58 ` [RFC v2 4/6] eal: add unit tests for " Mattias Rönnblom
2024-04-25 8:58 ` [RFC v2 5/6] eal: add atomic bit operations Mattias Rönnblom
2024-04-25 10:25 ` Morten Brørup
2024-04-25 14:36 ` Mattias Rönnblom
2024-04-25 16:18 ` Morten Brørup
2024-04-26 9:39 ` Mattias Rönnblom [this message]
2024-04-26 12:00 ` Morten Brørup
2024-04-28 15:37 ` Mattias Rönnblom
2024-04-29 7:24 ` Morten Brørup
2024-04-30 16:52 ` Tyler Retzlaff
2024-04-25 8:58 ` [RFC v2 6/6] eal: add unit tests for atomic bit access functions Mattias Rönnblom
2024-04-25 18:05 ` [RFC v2 0/6] Improve EAL bit operations API Tyler Retzlaff
2024-04-26 11:17 ` Mattias Rönnblom
2024-04-26 21:35 ` Patrick Robb
2024-03-02 13:53 ` [RFC 2/7] eal: add generic bit manipulation macros Mattias Rönnblom
2024-03-04 8:16 ` Heng Wang
2024-03-04 15:41 ` Mattias Rönnblom
2024-03-04 16:42 ` Tyler Retzlaff
2024-03-05 18:08 ` Mattias Rönnblom
2024-03-05 18:22 ` Tyler Retzlaff
2024-03-05 20:02 ` Mattias Rönnblom
2024-03-05 20:53 ` Tyler Retzlaff
2024-03-02 13:53 ` [RFC 3/7] eal: add bit manipulation functions which read or write once Mattias Rönnblom
2024-03-02 13:53 ` [RFC 4/7] eal: add generic once-type bit operations macros Mattias Rönnblom
2024-03-02 13:53 ` [RFC 5/7] eal: add atomic bit operations Mattias Rönnblom
2024-03-02 13:53 ` [RFC 6/7] eal: add generic " Mattias Rönnblom
2024-03-02 13:53 ` [RFC 7/7] eal: deprecate relaxed family of " Mattias Rönnblom
2024-03-02 17:07 ` Stephen Hemminger
2024-03-03 6:30 ` Mattias Rönnblom
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