From: Peter Zijlstra <peterz@infradead.org>
To: Alexander Sverdlin <alexander.sverdlin@nokia.com>
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 15:57:58 +0100 [thread overview]
Message-ID: <YBLQ9hbj8Zafjz+c@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <b00f945a-1278-5fd2-321c-6ea5f07be128@nokia.com>
On Thu, Jan 28, 2021 at 12:52:22PM +0100, Alexander Sverdlin wrote:
> Hello Peter,
>
> On 28/01/2021 12:33, Peter Zijlstra wrote:
> > This, from commit 6b07d38aaa52 ("MIPS: Octeon: Use optimized memory
> > barrier primitives."):
> >
> > #define smp_mb__before_llsc() smp_wmb()
> > #define __smp_mb__before_llsc() __smp_wmb()
> >
> > is also dodgy as hell and really wants a comment too. I'm not buying the
> > Changelog of that commit either, __smp_mb__before_llsc should also
> > ensure the LL cannot happen earlier, but SYNCW has no effect on loads.
> > So what stops the load from being speculated?
>
> hmm, the commit message you point to above, says:
>
> "Since Octeon does not do speculative reads, this functions as a full barrier."
So then the only difference between SYNC and SYNCW is a pipeline drain?
I still worry about the transitivity thing.. ISTR that being a sticky
point back then too.
next prev parent reply other threads:[~2021-01-28 15:00 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
2021-01-28 11:33 ` Peter Zijlstra
2021-01-28 11:52 ` Alexander Sverdlin
2021-01-28 14:57 ` Peter Zijlstra [this message]
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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