linux-kernel - Re: [PATCH v2 15/31] arm64: SMP support

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Message-ID: <20120817093912.GW11011@atomide.com>
Date:	Fri, 17 Aug 2012 02:39:12 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Will Deacon <Will.Deacon@....com>,
	Marc Zyngier <Marc.Zyngier@....com>
Subject: Re: [PATCH v2 15/31] arm64: SMP support

* Catalin Marinas <catalin.marinas@....com> [120817 02:33]:
> On Fri, Aug 17, 2012 at 10:21:33AM +0100, Tony Lindgren wrote:
> > * Catalin Marinas <catalin.marinas@....com> [120814 11:05]:
> > > This patch adds SMP initialisation and spinlocks implementation for
> > > AArch64. The spinlock support uses the new load-acquire/store-release
> > > instructions to avoid explicit barriers. The architecture also specifies
> > > that an event is automatically generated when clearing the exclusive
> > > monitor state to wake up processors in WFE, so there is no need for an
> > > explicit DSB/SEV instruction sequence. The SEVL instruction is used to
> > > set the exclusive monitor locally as there is no conditional WFE and a
> > > branch is more expensive.
> > 
> > Do we always have SMP hardware on arm64? Or are we going to need to
> > again add smp_on_up support later on?
> 
> There isn't anything in the architecture specs that mandates multiple
> cores but given the current trend it's very likely that we'll always
> have MP.
> 
> An improvement in AArch64 is that we can use the SMP cache/TLB ops (the
> inner shareable variants) even on a UP system so there is no need for
> run-time code patching for correct execution.

That's good to hear!

Tony
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