[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20160126101927.GD6357@twins.programming.kicks-ass.net>
Date: Tue, 26 Jan 2016 11:19:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Will Deacon <will.deacon@....com>,
Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
linux-arch@...r.kernel.org,
Andrew Cooper <andrew.cooper3@...rix.com>,
Russell King - ARM Linux <linux@....linux.org.uk>,
virtualization@...ts.linux-foundation.org,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
Joe Perches <joe@...ches.com>,
David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
adi-buildroot-devel@...ts.sourceforge.net,
linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
xen-devel@...ts.xenproject.org, Ralf Baechle <ralf@...ux-mips.org>,
Ingo Molnar <mingo@...nel.org>, ddaney.cavm@...il.com,
james.hogan@...tec.com, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
On Mon, Jan 25, 2016 at 10:03:22PM -0800, Paul E. McKenney wrote:
> On Mon, Jan 25, 2016 at 04:42:43PM +0000, Will Deacon wrote:
> > On Fri, Jan 15, 2016 at 01:58:53PM -0800, Paul E. McKenney wrote:
> > > On Fri, Jan 15, 2016 at 10:27:14PM +0100, Peter Zijlstra wrote:
> > > > Yes, that seems a good start. But yesterday you raised the 'fun' point
> > > > of two globally ordered sequences connected by a single local link.
> > >
> > > The conclusion that I am slowly coming to is that litmus tests should
> > > not be thought of as linear chains, but rather as cycles. If you think
> > > of it as a cycle, then it doesn't matter where the local link is, just
> > > how many of them and how they are connected.
> >
> > Do you have some examples of this? I'm struggling to make it work in my
> > mind, or are you talking specifically in the context of the kernel
> > memory model?
>
> Now that you mention it, maybe it would be best to keep the transitive
> and non-transitive separate for the time being anyway. Just because it
> might be possible to deal with does not necessarily mean that we should
> be encouraging it. ;-)
So isn't smp_mb__after_unlock_lock() exactly such a scenario? And would
not someone trying to implement RCsc locks using locally transitive
RELEASE/ACQUIRE operations need exactly this stuff?
That is, I am afraid we need to cover the mix of local and global
transitive operations at least in overview.
Powered by blists - more mailing lists