From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: percpu: Make this_cpu accessors pre-empt safe
Date: Fri, 20 Mar 2015 18:02:29 +0000 [thread overview]
Message-ID: <20150320180228.GI1474@arm.com> (raw)
In-Reply-To: <20150319163955.GG25967@leverpostej>
On Thu, Mar 19, 2015 at 04:39:55PM +0000, Mark Rutland wrote:
> On Thu, Mar 19, 2015 at 04:27:53PM +0000, Will Deacon wrote:
> > (3) Preemption isn't actually an issue here -- CPU migration is. I'd
> > expect that to be a lot rarer.
>
> That's not true: in a read-modify-cmpxchg loop (even on a UP system) if
> you get preempted at the end of the read and another thread modifies
> your datastructure, then your subsequent cmpxchg will fail. So any
> preemption could cause you to have to retry, so you want to miminise
> potential preemptions.
>
> Note that this is a performance argument rather than a correctness
> argument.
My argument is more that a migration will always break the cmpxchg, whereas
preemption doesn't necessarily.
Steve -- can you respin this using preempt_enable everywhere please?
Will
next prev parent reply other threads:[~2015-03-20 18:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-19 14:52 [PATCH] arm64: percpu: Make this_cpu accessors pre-empt safe Steve Capper
2015-03-19 15:44 ` Mark Rutland
2015-03-19 15:55 ` Steve Capper
2015-03-19 16:23 ` Mark Rutland
2015-03-19 16:00 ` Will Deacon
2015-03-19 16:11 ` Mark Rutland
2015-03-19 16:27 ` Will Deacon
2015-03-19 16:39 ` Mark Rutland
2015-03-20 18:02 ` Will Deacon [this message]
2015-03-22 14:51 ` [PATCH V2] " Steve Capper
2015-03-23 10:17 ` Will Deacon
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