From: Chris Metcalf <cmetcalf@ezchip.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will.deacon@arm.com>,
Oleg Nesterov <oleg@redhat.com>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
"mtk.manpages@gmail.com" <mtk.manpages@gmail.com>,
"dvhart@infradead.org" <dvhart@infradead.org>,
"dave@stgolabs.net" <dave@stgolabs.net>,
"Vineet.Gupta1@synopsys.com" <Vineet.Gupta1@synopsys.com>,
"ralf@linux-mips.org" <ralf@linux-mips.org>,
"ddaney@caviumnetworks.com" <ddaney@caviumnetworks.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Russell King - ARM Linux <linux@arm.linux.org.uk>,
Richard Henderson <rth@twiddle.net>
Subject: Re: futex atomic vs ordering constraints
Date: Fri, 4 Sep 2015 13:25:55 -0400 [thread overview]
Message-ID: <55E9D423.1090803@ezchip.com> (raw)
In-Reply-To: <CA+55aFzbycJ5UXYvwROcr6RG5_+Xxy2YaMn+Q3DksdNp+T3+bg@mail.gmail.com>
On 09/02/2015 05:18 PM, Linus Torvalds wrote:
> For example, on x86, the locked instructions are obviously already
> sufficiently strong, but even if they weren't, kernel entry/exit is
> documented to be a serializing instruction (which is something
> insanely much stronger than just memory ordering). And I suspect there
> are similar issues on a lot of architectures where the memory ordering
> is done by the core, but the cache subsystem is strongly ordered (ie
> saen good SMP systems - so it sounds like tile needs the smp_mb()'s,
> but I would almost suspect that POWER and ARM might *not* need them).
Because POWER and ARM have serializing kernel entry/exit?
I think tile has relatively conventional cache/memory semantics,
but it's certainly true there is implicit memory ordering guarantee
for kernel entry/exit.
--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com
next prev parent reply other threads:[~2015-09-04 17:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-26 18:16 Peter Zijlstra
2015-08-29 1:33 ` Davidlohr Bueso
2015-09-01 16:38 ` Peter Zijlstra
2015-09-01 16:31 ` Will Deacon
2015-09-01 16:42 ` Peter Zijlstra
2015-09-01 16:47 ` Will Deacon
2015-09-01 19:05 ` Thomas Gleixner
2015-09-02 12:55 ` Peter Zijlstra
2015-09-02 16:10 ` Chris Metcalf
2015-09-02 17:00 ` Peter Zijlstra
2015-09-02 17:25 ` Chris Metcalf
2015-09-02 21:18 ` Linus Torvalds
2015-09-04 17:25 ` Chris Metcalf [this message]
2015-09-05 17:53 ` Peter Zijlstra
2015-09-07 9:30 ` Will Deacon
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