From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Burton <paul.burton@imgtec.com>,
linux-mips@vger.kernel.org,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] MIPS: Octeon: Implement __smp_store_release()
Date: Thu, 28 Jan 2021 08:27:29 +0100 [thread overview]
Message-ID: <aace6ff1-9ddf-15af-3c0a-378c53c59acb@nokia.com> (raw)
In-Reply-To: <YBHp4139X+p+4IZ+@hirez.programming.kicks-ass.net>
Hello Peter,
On 27/01/2021 23:32, Peter Zijlstra wrote:
>> Link: https://lore.kernel.org/lkml/5644D08D.4080206@caviumnetworks.com/
please, check the discussion pointed by the link above...
>> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
>> ---
>> arch/mips/include/asm/barrier.h | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
>> index 49ff172..24c3f2c 100644
>> --- a/arch/mips/include/asm/barrier.h
>> +++ b/arch/mips/include/asm/barrier.h
>> @@ -113,6 +113,15 @@ static inline void wmb(void)
>> ".set arch=octeon\n\t" \
>> "syncw\n\t" \
>> ".set pop" : : : "memory")
>> +
>> +#define __smp_store_release(p, v) \
>> +do { \
>> + compiletime_assert_atomic_type(*p); \
>> + __smp_wmb(); \
>> + __smp_rmb(); \
>> + WRITE_ONCE(*p, v); \
>> +} while (0)
> This is wrong in general since smp_rmb() will only provide order between
> two loads and smp_store_release() is a store.
>
> If this is correct for all MIPS, this needs a giant comment on exactly
> how that smp_rmb() makes sense here.
... the macro is provided for Octeon only, and __smp_rmb() is actually a NOP
there, but I thought to "document" the flow of thoughts from the discussion
above by including it anyway.
--
Best regards,
Alexander Sverdlin.
next prev parent reply other threads:[~2021-01-28 7:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 20:36 [PATCH 0/6] MIPS: qspinlock: Try to reduce reduce the spinlock regression Alexander A Sverdlin
2021-01-27 20:36 ` [PATCH 1/6] MIPS: Octeon: Implement __smp_store_release() Alexander A Sverdlin
2021-01-27 22:32 ` Peter Zijlstra
2021-01-28 7:27 ` Alexander Sverdlin [this message]
2021-01-28 11:33 ` Peter Zijlstra
2021-01-28 11:52 ` Alexander Sverdlin
2021-01-28 14:57 ` Peter Zijlstra
2021-01-28 15:15 ` Peter Zijlstra
2021-01-28 12:09 ` Alexander Sverdlin
2021-01-28 15:04 ` Peter Zijlstra
2021-01-27 20:36 ` [PATCH 2/6] MIPS: Implement atomic_cmpxchg_relaxed() Alexander A Sverdlin
2021-01-27 20:36 ` [PATCH 3/6] MIPS: Octeon: qspinlock: Flush write buffer Alexander A Sverdlin
2021-01-27 22:34 ` Peter Zijlstra
2021-01-28 7:29 ` Alexander Sverdlin
2021-01-28 11:35 ` Peter Zijlstra
2021-01-28 12:13 ` Alexander Sverdlin
2021-01-28 15:26 ` Peter Zijlstra
2021-01-27 20:36 ` [PATCH 4/6] MIPS: Octeon: qspinlock: Exclude mmiowb() Alexander A Sverdlin
2021-01-27 22:35 ` Peter Zijlstra
2021-01-27 20:36 ` [PATCH 5/6] MIPS: Provide {atomic_}xchg_relaxed() Alexander A Sverdlin
2021-01-27 20:36 ` [PATCH 6/6] MIPS: cmpxchg: Use cmpxchg_local() for {cmp_}xchg_small() Alexander A Sverdlin
2021-01-27 22:37 ` Peter Zijlstra
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