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From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
To: linux-arm-kernel@lists.infradead.org
Subject: [v3,11/41] mips: reuse asm-generic/barrier.h
Date: Thu, 14 Jan 2016 16:47:53 -0800	[thread overview]
Message-ID: <20160115004753.GN3818@linux.vnet.ibm.com> (raw)
In-Reply-To: <56983054.4070807@imgtec.com>

On Thu, Jan 14, 2016 at 03:33:40PM -0800, Leonid Yegoshin wrote:
> 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)

Fair enough!  ;-)

> >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).

So smp_mb() can be SYNC_MB.  However, mb() needs to be SYNC for MMIO
purposes, correct?

> >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.

Indeed!

> >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.

Looks to me like smp_mb() can be SYNC_MB, then.

> 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.

So you need to build a different kernel for some types of MIPS systems?
Or do you do boot-time rewriting, like a number of other arches do?

							Thanx, Paul

  reply	other threads:[~2016-01-15  0:47 UTC|newest]

Thread overview: 153+ 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
2016-01-26 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
2016-01-15  0:47                                   ` Paul E. McKenney [this message]
2016-01-15  1:07                                     ` Leonid Yegoshin
2016-01-27 11:26                                       ` Maciej W. Rozycki
2016-01-28  0:58                                         ` Leonid Yegoshin
     [not found]                                         ` <56A9656D.3080707@imgtec.com>
2016-01-29 13:38                                           ` Maciej W. Rozycki
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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