From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Tom Musta <tommusta@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
Anton Blanchard <anton@samba.org>, Torsten Duwe <duwe@lst.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks
Date: Mon, 10 Feb 2014 13:54:13 +1100 [thread overview]
Message-ID: <1392000853.3996.13.camel@pasglop> (raw)
In-Reply-To: <52F3E255.5050906@gmail.com>
On Thu, 2014-02-06 at 13:28 -0600, Tom Musta wrote:
> My read is consistent with Torsten's ... this looks like a bad idea.
>
> Look at the RTL for sthcx. on page 692 (Power ISA V2.06) and you will
> see this:
>
> if RESERVE then
> if RESERVE_LENGTH = 2 then
> ...
> else
> undefined_case <- 1
> else
> ...
>
> A legal implementation might never perform the store.
This is an area where we definitely want to check with the implementors
and if the implementations happen to do what we want (they likely do),
get the architecture changed for future chips and use it anyway.
There's a a *significant* benefit in avoiding an atomic operation in the
unlock case .
The reservation mechanism being based on a granule that is generally a
cache line, I doubt implementations will ever check the actual access
size, but we need to double check.
Cheers,
Ben.
next prev parent reply other threads:[~2014-02-10 2:55 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-06 10:37 [PATCH] Convert powerpc simple spinlocks into ticket locks Torsten Duwe
2014-02-06 15:53 ` Benjamin Herrenschmidt
2014-02-06 16:38 ` Peter Zijlstra
2014-02-06 17:37 ` Torsten Duwe
2014-02-06 18:08 ` Peter Zijlstra
2014-02-06 19:28 ` Tom Musta
2014-02-10 2:54 ` Benjamin Herrenschmidt [this message]
2014-02-07 8:24 ` Torsten Duwe
2014-02-06 20:19 ` Scott Wood
2014-02-07 9:02 ` Torsten Duwe
2014-02-07 10:31 ` Peter Zijlstra
2014-02-07 10:36 ` Peter Zijlstra
2014-02-07 10:45 ` Peter Zijlstra
2014-02-07 11:49 ` Torsten Duwe
2014-02-07 12:28 ` Peter Zijlstra
2014-02-07 15:18 ` Peter Zijlstra
2014-02-07 15:43 ` Peter Zijlstra
2014-02-07 17:08 ` Torsten Duwe
2014-02-07 17:19 ` Peter Zijlstra
2014-02-07 15:51 ` Kumar Gala
2014-02-07 16:10 ` Peter Zijlstra
2014-02-10 3:05 ` Benjamin Herrenschmidt
2014-02-10 3:02 ` Benjamin Herrenschmidt
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