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Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
- Date: Tue, 26 Jan 2016 16:57:30 -0800
- Cc: linux-mips <linux-mips@xxxxxxxxxxxxxx>, "linux-ia64@xxxxxxxxxxxxxxx" <linux-ia64@xxxxxxxxxxxxxxx>, "Michael S. Tsirkin" <mst@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Peter Anvin <hpa@xxxxxxxxx>, sparclinux@xxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, "linux-arch@xxxxxxxxxxxxxxx" <linux-arch@xxxxxxxxxxxxxxx>, linux-s390 <linux-s390@xxxxxxxxxxxxxxx>, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, linux-sh@xxxxxxxxxxxxxxx, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxx>, linux-xtensa@xxxxxxxxxxxxxxxx, James Hogan <james.hogan@xxxxxxxxxx>, uml-devel <user-mode-linux-devel@xxxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, Boqun Feng <boqun.feng@xxxxxxxxx>, adi-buildroot-devel@xxxxxxxxxxxxxxxxxxxxx, Leonid Yegoshin <Leonid.Yegoshin@xxxxxxxxxx>, David Daney <ddaney.cavm@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-metag@xxxxxxxxxxxxxxx, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Ralf Baechle <ralf@xxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Joe Perches <joe@xxxxxxxxxxx>, ppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>, David Miller <davem@xxxxxxxxxxxxx>
- Delivery-date: Wed, 27 Jan 2016 00:57:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Tue, Jan 26, 2016 at 03:45:23PM -0800, Linus Torvalds wrote:
> On Tue, Jan 26, 2016 at 3:29 PM, Paul E. McKenney
> <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > No trailing data-dependent read, so agreed, no smp_read_barrier_depends()
> > needed. That said, I believe that we should encourage rcu_dereference*()
> > or lockless_dereference() instead of READ_ONCE() for documentation
> > reasons, though.
>
> I agree that that is likely the right thing to do in pretty much all
> situations.
>
> In theory, there might be performance situations where we'd want to
> actively avoid the smp_read_barrier_depends() inherent in those, but
> considering that it's only a performance issue on alpha, and we
> probably have all of two or three people using Linux on alpha, it's a
> pretty theoretical performance worry.
Agreed!
Thanx, Paul
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- References:
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
- Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
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