From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
To: <paulmck@linux.vnet.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
<linux-kernel@vger.kernel.org>, "Arnd Bergmann" <arnd@arndb.de>,
<linux-arch@vger.kernel.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Russell King - ARM Linux <linux@arm.linux.org.uk>,
<virtualization@lists.linux-foundation.org>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
"H. Peter Anvin" <hpa@zytor.com>, Joe Perches <joe@perches.com>,
David Miller <davem@davemloft.net>, <linux-ia64@vger.kernel.org>,
<linuxppc-dev@lists.ozlabs.org>, <linux-s390@vger.kernel.org>,
<sparclinux@vger.kernel.org>,
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<adi-buildroot-devel@lists.sourceforge.net>,
<linux-sh@vger.kernel.org>, <linux-xtensa@linux-xtensa.org>,
<xen-devel@lists.xenproject.org>,
"Ralf Baechle" <ralf@linux-mips.org>,
Ingo Molnar <mingo@kernel.org>, <ddaney.cavm@gmail.com>,
<james.hogan@imgtec.com>, Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
Date: Thu, 14 Jan 2016 15:33:40 -0800 [thread overview]
Message-ID: <56983054.4070807@imgtec.com> (raw)
In-Reply-To: <20160114225510.GJ3818@linux.vnet.ibm.com>
On 01/14/2016 02:55 PM, Paul E. McKenney wrote:
> OK, so it looks like Will was asking not about WRC+addr+addr, but instead
> about WRC+sync+addr.
(He actually asked twice about this and that too but skip this)
> I am guessing that the manual's "Older instructions which must be globally
> performed when the SYNC instruction completes" provides the equivalent
> of ARM/Power A-cumulativity, which can be thought of as transitivity
> backwards in time. This leads me to believe that your smp_mb() needs
> to use SYNC rather than SYNC_MB, as was the subject of earlier spirited
> discussion in this thread.
Don't be fooled here by words "ordered" and "completed" - it is HW
design items and actually written poorly.
Just assume that SYNC_MB is absolutely the same as SYNC for any CPU and
coherent device (besides performance). The difference can be in
non-coherent devices because SYNC actually tries to make a barrier for
them too. In some SoCs it is just the same because there is no need to
barrier a non-coherent device (device register access usually strictly
ordered... if there is no bridge in between).
>
> Suppose you have something like this:
> ...
> Does your hardware guarantee that it is not possible for all of r0,
> r1, r2, and r3 to be equal to zero at the end of the test, assuming
> that a, b, c, and d are all initially zero, and the four functions
> above run concurrently?
It is assumed to be so from Arch point of view. HW bugs are possible, of
course.
> Another (more academic) case is this one, with x and y initially zero:
>
> ...
> Does SYNC_MB() prohibit r1 == 1 && r2 == 0 && r3 == 1 && r4 == 0?
It is assumed to be so from Arch point of view. HW bugs are possible, of
course.
Note: I am not sure about ANY past MIPS R2 CPU because that stuff is
implemented some time but nobody made it in Linux kernel (it was used by
some vendor for non-Linux system). For that reason my patch for
lightweight SYNCs has an option - implement it or implement a generic
SYNC. It is possible that some vendor did it in different way but nobody
knows or test it. But as a minimum - SYNC must be implemented in
spinlocks/atomics/bitops, in recent P5600 it is proven that read can
pass write in atomics.
MIPS R6 is a different story, I verified lightweight SYNCs from the
beginning and it also should use SYNCs.
- Leonid.
next prev parent reply other threads:[~2016-01-14 23:33 UTC|newest]
Thread overview: 155+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-10 14:16 [PATCH v3 00/41] arch: barrier cleanup + barriers for virt Michael S. Tsirkin
2016-01-10 14:16 ` [PATCH v3 01/41] lcoking/barriers, arch: Use smp barriers in smp_store_release() Michael S. Tsirkin
2016-01-12 16:28 ` Paul E. McKenney
2016-01-12 18:40 ` Michael S. Tsirkin
2016-01-10 14:16 ` [PATCH v3 02/41] asm-generic: guard smp_store_release/load_acquire Michael S. Tsirkin
2016-01-10 14:16 ` [PATCH v3 03/41] ia64: rename nop->iosapic_nop Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 04/41] ia64: reuse asm-generic/barrier.h Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 05/41] powerpc: " Michael S. Tsirkin
2016-01-12 16:31 ` Paul E. McKenney
2016-01-10 14:17 ` [PATCH v3 06/41] s390: " Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 07/41] sparc: " Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 08/41] arm: " Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 09/41] arm64: " Michael S. Tsirkin
2016-01-10 14:17 ` [PATCH v3 10/41] metag: " Michael S. Tsirkin
2016-01-10 14:18 ` [PATCH v3 11/41] mips: " Michael S. Tsirkin
2016-01-12 1:14 ` [v3,11/41] " Leonid Yegoshin
2016-01-12 8:43 ` Michael S. Tsirkin
2016-01-12 9:51 ` Peter Zijlstra
2016-01-12 9:27 ` Peter Zijlstra
2016-01-12 10:25 ` Peter Zijlstra
2016-01-12 10:40 ` Peter Zijlstra
2016-01-12 11:41 ` Will Deacon
2016-01-12 20:45 ` Leonid Yegoshin
2016-01-12 21:40 ` Peter Zijlstra
2016-01-13 0:21 ` Leonid Yegoshin
2016-01-13 10:45 ` Will Deacon
2016-01-13 19:02 ` Leonid Yegoshin
2016-01-13 20:48 ` Peter Zijlstra
2016-01-13 20:58 ` Leonid Yegoshin
2016-01-14 12:04 ` Will Deacon
2016-01-14 16:16 ` Paul E. McKenney
2016-01-14 19:42 ` Leonid Yegoshin
2016-01-14 20:15 ` Peter Zijlstra
2016-01-14 20:36 ` Paul E. McKenney
2016-01-14 20:46 ` Peter Zijlstra
2016-01-14 20:46 ` Leonid Yegoshin
2016-01-14 21:34 ` Paul E. McKenney
2016-01-14 21:45 ` Leonid Yegoshin
2016-01-14 22:24 ` Paul E. McKenney
2016-01-14 23:04 ` Leonid Yegoshin
2016-01-14 20:12 ` Leonid Yegoshin
2016-01-14 20:48 ` Paul E. McKenney
2016-01-14 21:24 ` Leonid Yegoshin
2016-01-14 22:20 ` Paul E. McKenney
2016-01-15 9:57 ` Will Deacon
2016-01-15 18:54 ` Leonid Yegoshin
2016-01-26 10:24 ` Peter Zijlstra
2016-01-26 10:32 ` Peter Zijlstra
2016-01-26 11:09 ` Will Deacon
2016-01-26 20:11 ` Paul E. McKenney
2016-01-27 8:35 ` [PATCH] documentation: Add disclaimer Peter Zijlstra
2016-01-27 10:11 ` Will Deacon
2016-04-14 21:40 ` Paul E. McKenney
2016-01-27 14:57 ` David Howells
2016-01-27 23:35 ` Paul E. McKenney
2016-01-28 20:02 ` David Howells
2016-04-14 21:40 ` Paul E. McKenney
2016-01-26 19:44 ` [v3,11/41] mips: reuse asm-generic/barrier.h Paul E. McKenney
2016-01-18 8:19 ` Herbert Xu
2016-01-18 15:46 ` Paul E. McKenney
2016-01-26 16:52 ` Boqun Feng
2016-01-26 17:22 ` Peter Zijlstra
2016-01-26 19:44 ` Linus Torvalds
2016-01-26 20:10 ` Paul E. McKenney
2016-01-26 22:15 ` Linus Torvalds
2016-01-26 22:33 ` Linus Torvalds
2016-01-26 23:29 ` Paul E. McKenney
2016-01-26 23:45 ` Linus Torvalds
2016-01-27 0:57 ` Paul E. McKenney
2016-01-27 2:04 ` Boqun Feng
2016-01-27 23:30 ` Paul E. McKenney
2016-01-27 7:51 ` Peter Zijlstra
2016-01-27 8:05 ` Linus Torvalds
2016-01-26 19:51 ` Paul E. McKenney
2016-01-13 22:26 ` Leonid Yegoshin
2016-01-14 9:24 ` Michael S. Tsirkin
2016-01-14 12:14 ` Will Deacon
2016-01-14 19:28 ` Leonid Yegoshin
2016-01-14 20:34 ` Paul E. McKenney
2016-01-14 21:01 ` Leonid Yegoshin
2016-01-14 21:29 ` Paul E. McKenney
2016-01-14 21:36 ` Leonid Yegoshin
2016-01-14 22:55 ` Paul E. McKenney
2016-01-14 23:33 ` Leonid Yegoshin [this message]
2016-01-15 0:47 ` Paul E. McKenney
2016-01-15 1:07 ` Leonid Yegoshin
2016-01-27 11:26 ` Maciej W. Rozycki
2016-01-28 0:48 ` Leonid Yegoshin
2016-01-29 13:38 ` Maciej W. Rozycki
2016-01-28 0:58 ` Leonid Yegoshin
2016-01-27 10:40 ` Ralf Baechle
2016-01-27 12:09 ` Maciej W. Rozycki
2016-01-15 10:24 ` Will Deacon
2016-01-15 17:54 ` Paul E. McKenney
2016-01-15 19:28 ` Paul E. McKenney
2016-01-25 14:41 ` Will Deacon
2016-01-26 1:06 ` Paul E. McKenney
2016-01-26 12:10 ` Will Deacon
2016-01-26 23:37 ` Paul E. McKenney
2016-01-27 10:23 ` Will Deacon
2016-01-15 8:55 ` Peter Zijlstra
2016-01-15 9:13 ` Peter Zijlstra
2016-01-15 17:46 ` Paul E. McKenney
2016-01-15 21:27 ` Peter Zijlstra
2016-01-15 21:58 ` Paul E. McKenney
2016-01-25 16:42 ` Will Deacon
2016-01-26 6:03 ` Paul E. McKenney
2016-01-26 10:19 ` Peter Zijlstra
2016-01-26 20:13 ` Paul E. McKenney
2016-01-27 8:39 ` Peter Zijlstra
2016-01-26 12:16 ` Will Deacon
2016-01-26 14:35 ` Boqun Feng
2016-01-26 19:58 ` Paul E. McKenney
2016-01-27 10:25 ` Will Deacon
2016-01-27 23:32 ` Paul E. McKenney
2016-01-15 17:39 ` Paul E. McKenney
2016-01-15 21:29 ` Peter Zijlstra
2016-01-15 22:01 ` Paul E. McKenney
2016-01-25 18:02 ` Will Deacon
2016-01-26 6:12 ` Paul E. McKenney
2016-01-26 10:15 ` Peter Zijlstra
2016-01-10 14:18 ` [PATCH v3 12/41] x86/um: " Michael S. Tsirkin
2016-01-10 14:18 ` [PATCH v3 13/41] x86: " Michael S. Tsirkin
2016-01-12 14:10 ` Thomas Gleixner
2016-01-10 14:18 ` [PATCH v3 14/41] asm-generic: add __smp_xxx wrappers Michael S. Tsirkin
2016-01-10 14:18 ` [PATCH v3 15/41] powerpc: define __smp_xxx Michael S. Tsirkin
2016-01-10 14:18 ` [PATCH v3 16/41] arm64: " Michael S. Tsirkin
2016-01-10 14:18 ` [PATCH v3 17/41] arm: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 18/41] blackfin: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 19/41] ia64: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 20/41] metag: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 21/41] mips: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 22/41] s390: " Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 23/41] sh: define __smp_xxx, fix smp_store_mb for !SMP Michael S. Tsirkin
2016-01-10 14:19 ` [PATCH v3 24/41] sparc: define __smp_xxx Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 25/41] tile: " Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 26/41] xtensa: " Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 27/41] x86: " Michael S. Tsirkin
2016-01-12 14:11 ` Thomas Gleixner
2016-01-10 14:20 ` [PATCH v3 28/41] asm-generic: implement virt_xxx memory barriers Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 29/41] Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb" Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 30/41] virtio_ring: update weak barriers to use virt_xxx Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 31/41] sh: support 1 and 2 byte xchg Michael S. Tsirkin
2016-01-10 14:20 ` [PATCH v3 32/41] sh: move xchg_cmpxchg to a header by itself Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 33/41] virtio_ring: use virt_store_mb Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 34/41] checkpatch.pl: add missing memory barriers Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 35/41] checkpatch: check for __smp outside barrier.h Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 36/41] checkpatch: add virt barriers Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 37/41] xenbus: use virt_xxx barriers Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 38/41] xen/io: " Michael S. Tsirkin
2016-01-10 14:21 ` [PATCH v3 39/41] xen/events: " Michael S. Tsirkin
2016-01-11 11:12 ` David Vrabel
2016-01-10 14:22 ` [PATCH v3 40/41] s390: use generic memory barriers Michael S. Tsirkin
2016-01-10 14:22 ` [PATCH v3 41/41] s390: more efficient smp barriers Michael S. Tsirkin
2016-01-12 12:50 ` [PATCH v3 00/41] arch: barrier cleanup + barriers for virt Peter Zijlstra
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