From: Peter Zijlstra <peterz@infradead•org>
To: Pan Xinhui <xinhui@linux•vnet.ibm.com>
Cc: linux-kernel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
benh@kernel•crashing.org, paulus@samba•org, mpe@ellerman•id.au,
boqun.feng@gmail•com, paulmck@linux•vnet.ibm.com,
tglx@linutronix•de
Subject: Re: [PATCH V3] powerpc: Implement {cmp}xchg for u8 and u16
Date: Mon, 25 Apr 2016 17:37:10 +0200 [thread overview]
Message-ID: <20160425153710.GG3448@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <571DED2B.8060600@linux.vnet.ibm.com>
On Mon, Apr 25, 2016 at 06:10:51PM +0800, Pan Xinhui wrote:
> > So I'm not actually _that_ familiar with the PPC LL/SC implementation;
> > but there are things a CPU can do to optimize these loops.
> >
> > For example, a CPU might choose to not release the exclusive hold of the
> > line for a number of cycles, except when it passes SC or an interrupt
> > happens. This way there's a smaller chance the SC fails and inhibits
> > forward progress.
> I am not sure if there is such hardware optimization.
So I think the hardware must do _something_, otherwise competing cores
doing load-exlusive could life-lock a system, each one endlessly
breaking the exclusive ownership of the other and the store-conditional
always failing.
Of course, there are such implementations, and they tend to have to put
in explicit backoff loops; however, IIRC, PPC doesn't need that. (See
ARC for an example that needs to do this.)
next prev parent reply other threads:[~2016-04-25 15:37 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-19 6:29 [PATCH V2] powerpc: Implement {cmp}xchg for u8 and u16 Pan Xinhui
2016-04-19 9:18 ` Boqun Feng
2016-04-20 3:39 ` Pan Xinhui
2016-04-20 13:24 ` [PATCH V3] " Pan Xinhui
2016-04-20 14:24 ` Peter Zijlstra
2016-04-21 15:35 ` Pan Xinhui
2016-04-21 15:52 ` Boqun Feng
2016-04-22 1:59 ` Pan Xinhui
2016-04-22 3:16 ` Boqun Feng
2016-04-21 16:13 ` Peter Zijlstra
2016-04-25 10:10 ` Pan Xinhui
2016-04-25 15:37 ` Peter Zijlstra [this message]
2016-04-26 11:35 ` Pan Xinhui
2016-04-27 9:16 ` [PATCH V4] " Pan Xinhui
2016-04-27 13:58 ` Boqun Feng
2016-04-27 14:16 ` Boqun Feng
2016-04-27 14:50 ` Boqun Feng
2016-04-27 14:59 ` Boqun Feng
2016-04-28 10:21 ` Pan Xinhui
2016-04-28 7:59 ` Peter Zijlstra
2016-04-28 10:21 ` Pan Xinhui
2016-11-25 0:04 ` [V4] " Michael Ellerman
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