From: Will Deacon <will.deacon@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, Victor Kaplansky <VICTORK@il.ibm.com>, Oleg Nesterov <oleg@redhat.com>, Anton Blanchard <anton@samba.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Frederic Weisbecker <fweisbec@gmail.com>, LKML <linux-kernel@vger.kernel.org>, Linux PPC dev <linuxppc-dev@ozlabs.org>, Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>, Michael Ellerman <michael@ellerman.id.au>, Michael Neuling <mikey@neuling.org>, "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>, "schwidefsky@de.ibm.com" <schwidefsky@de.ibm.com>, "heiko.carstens@de.ibm.com" <heiko.carstens@de.ibm.com> Subject: Re: [RFC] arch: Introduce new TSO memory barrier smp_tmb() Date: Wed, 6 Nov 2013 11:00:43 +0000 [thread overview] Message-ID: <20131106110043.GD21074@mudshark.cambridge.arm.com> (raw) In-Reply-To: <20131105184943.GY16117@laptop.programming.kicks-ass.net> On Tue, Nov 05, 2013 at 06:49:43PM +0000, Peter Zijlstra wrote: > On Tue, Nov 05, 2013 at 02:05:48PM +0000, Will Deacon wrote: > > > > + > > > > +#define smp_store_release(p, v) \ > > > > +do { \ > > > > + smp_mb(); \ > > > > + ACCESS_ONCE(p) = (v); \ > > > > +} while (0) > > > > + > > > > +#define smp_load_acquire(p, v) \ > > > > +do { \ > > > > + typeof(p) ___p1 = ACCESS_ONCE(p); \ > > > > + smp_mb(); \ > > > > + return ___p1; \ > > > > +} while (0) > > > > What data sizes do these accessors operate on? Assuming that we want > > single-copy atomicity (with respect to interrupts in the UP case), we > > probably want a check to stop people passing in things like structs. > > Fair enough; I think we should restrict to native word sizes same as we > do for atomics. > > Something like so perhaps: > > #ifdef CONFIG_64BIT > #define __check_native_word(t) (sizeof(t) == 4 || sizeof(t) == 8) Ok, if we want to support 32-bit accesses on 64-bit machines, that will complicate some of your assembly (more below). > #else > #define __check_native_word(t) (sizeof(t) == 4) > #endif > > #define smp_store_release(p, v) \ > do { \ > BUILD_BUG_ON(!__check_native_word(p)); \ > smp_mb(); \ > ACCESS_ONCE(p) = (v); \ > } while (0) > > > > > +#define smp_store_release(p, v) \ > > > > +do { \ > > > > + asm volatile ("stlr %w0 [%1]" : : "r" (v), "r" (&p) : "memory");\ > > > > Missing comma between the operands. Also, that 'w' output modifier enforces > > a 32-bit store (same early question about sizes). Finally, it might be more > > efficient to use "=Q" for the addressing mode, rather than take the address > > of p manually. > > so something like: > > asm volatile ("stlr %0, [%1]" : : "r" (v), "=Q" (p) : "memory"); > > ? > > My inline asm foo is horrid and I mostly get by with copy paste from a > semi similar existing form :/ Almost: you just need to drop the square brackets and make the memory location an output operand: asm volatile("stlr %1, %0" : "=Q" (p) : "r" (v) : "memory"); however, for a 32-bit access, you need to use an output modifier: asm volatile("stlr %w1, %0" : "=Q" (p) : "r" (v) : "memory"); so I guess a switch on sizeof(p) is required. > > Random other question: have you considered how these accessors should behave > > when presented with __iomem pointers? > > A what? ;-) Then let's go with Paul's suggestion of mandating __kernel, or the like (unless we need to worry about __user addresses for things like futexes?). Will
WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will.deacon@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: Michael Neuling <mikey@neuling.org>, Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>, "heiko.carstens@de.ibm.com" <heiko.carstens@de.ibm.com>, Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Linux PPC dev <linuxppc-dev@ozlabs.org>, Anton Blanchard <anton@samba.org>, Frederic Weisbecker <fweisbec@gmail.com>, Victor Kaplansky <VICTORK@il.ibm.com>, "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, "schwidefsky@de.ibm.com" <schwidefsky@de.ibm.com> Subject: Re: [RFC] arch: Introduce new TSO memory barrier smp_tmb() Date: Wed, 6 Nov 2013 11:00:43 +0000 [thread overview] Message-ID: <20131106110043.GD21074@mudshark.cambridge.arm.com> (raw) In-Reply-To: <20131105184943.GY16117@laptop.programming.kicks-ass.net> On Tue, Nov 05, 2013 at 06:49:43PM +0000, Peter Zijlstra wrote: > On Tue, Nov 05, 2013 at 02:05:48PM +0000, Will Deacon wrote: > > > > + > > > > +#define smp_store_release(p, v) \ > > > > +do { \ > > > > + smp_mb(); \ > > > > + ACCESS_ONCE(p) = (v); \ > > > > +} while (0) > > > > + > > > > +#define smp_load_acquire(p, v) \ > > > > +do { \ > > > > + typeof(p) ___p1 = ACCESS_ONCE(p); \ > > > > + smp_mb(); \ > > > > + return ___p1; \ > > > > +} while (0) > > > > What data sizes do these accessors operate on? Assuming that we want > > single-copy atomicity (with respect to interrupts in the UP case), we > > probably want a check to stop people passing in things like structs. > > Fair enough; I think we should restrict to native word sizes same as we > do for atomics. > > Something like so perhaps: > > #ifdef CONFIG_64BIT > #define __check_native_word(t) (sizeof(t) == 4 || sizeof(t) == 8) Ok, if we want to support 32-bit accesses on 64-bit machines, that will complicate some of your assembly (more below). > #else > #define __check_native_word(t) (sizeof(t) == 4) > #endif > > #define smp_store_release(p, v) \ > do { \ > BUILD_BUG_ON(!__check_native_word(p)); \ > smp_mb(); \ > ACCESS_ONCE(p) = (v); \ > } while (0) > > > > > +#define smp_store_release(p, v) \ > > > > +do { \ > > > > + asm volatile ("stlr %w0 [%1]" : : "r" (v), "r" (&p) : "memory");\ > > > > Missing comma between the operands. Also, that 'w' output modifier enforces > > a 32-bit store (same early question about sizes). Finally, it might be more > > efficient to use "=Q" for the addressing mode, rather than take the address > > of p manually. > > so something like: > > asm volatile ("stlr %0, [%1]" : : "r" (v), "=Q" (p) : "memory"); > > ? > > My inline asm foo is horrid and I mostly get by with copy paste from a > semi similar existing form :/ Almost: you just need to drop the square brackets and make the memory location an output operand: asm volatile("stlr %1, %0" : "=Q" (p) : "r" (v) : "memory"); however, for a 32-bit access, you need to use an output modifier: asm volatile("stlr %w1, %0" : "=Q" (p) : "r" (v) : "memory"); so I guess a switch on sizeof(p) is required. > > Random other question: have you considered how these accessors should behave > > when presented with __iomem pointers? > > A what? ;-) Then let's go with Paul's suggestion of mandating __kernel, or the like (unless we need to worry about __user addresses for things like futexes?). Will
next prev parent reply other threads:[~2013-11-06 11:00 UTC|newest] Thread overview: 212+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-10-22 23:54 perf events ring buffer memory barrier on powerpc Michael Neuling 2013-10-23 7:39 ` Victor Kaplansky 2013-10-23 7:39 ` Victor Kaplansky 2013-10-23 14:19 ` Frederic Weisbecker 2013-10-23 14:19 ` Frederic Weisbecker 2013-10-23 14:25 ` Frederic Weisbecker 2013-10-23 14:25 ` Frederic Weisbecker 2013-10-25 17:37 ` Peter Zijlstra 2013-10-25 17:37 ` Peter Zijlstra 2013-10-25 20:31 ` Michael Neuling 2013-10-25 20:31 ` Michael Neuling 2013-10-27 9:00 ` Victor Kaplansky 2013-10-27 9:00 ` Victor Kaplansky 2013-10-28 9:22 ` Peter Zijlstra 2013-10-28 9:22 ` Peter Zijlstra 2013-10-28 10:02 ` Frederic Weisbecker 2013-10-28 10:02 ` Frederic Weisbecker 2013-10-28 12:38 ` Victor Kaplansky 2013-10-28 12:38 ` Victor Kaplansky 2013-10-28 13:26 ` Peter Zijlstra 2013-10-28 13:26 ` Peter Zijlstra 2013-10-28 16:34 ` Paul E. McKenney 2013-10-28 16:34 ` Paul E. McKenney 2013-10-28 20:17 ` Oleg Nesterov 2013-10-28 20:17 ` Oleg Nesterov 2013-10-28 20:58 ` Victor Kaplansky 2013-10-28 20:58 ` Victor Kaplansky 2013-10-29 10:21 ` Peter Zijlstra 2013-10-29 10:21 ` Peter Zijlstra 2013-10-29 10:30 ` Peter Zijlstra 2013-10-29 10:30 ` Peter Zijlstra 2013-10-29 10:35 ` Peter Zijlstra 2013-10-29 10:35 ` Peter Zijlstra 2013-10-29 20:15 ` Oleg Nesterov 2013-10-29 20:15 ` Oleg Nesterov 2013-10-29 19:27 ` Vince Weaver 2013-10-29 19:27 ` Vince Weaver 2013-10-30 10:42 ` Peter Zijlstra 2013-10-30 10:42 ` Peter Zijlstra 2013-10-30 11:48 ` James Hogan 2013-10-30 11:48 ` James Hogan 2013-10-30 12:48 ` Peter Zijlstra 2013-10-30 12:48 ` Peter Zijlstra 2013-11-06 13:19 ` [tip:perf/core] tools/perf: Add required memory barriers tip-bot for Peter Zijlstra 2013-11-06 13:50 ` Vince Weaver 2013-11-06 14:00 ` Peter Zijlstra 2013-11-06 14:28 ` Peter Zijlstra 2013-11-06 14:55 ` Vince Weaver 2013-11-06 15:10 ` Peter Zijlstra 2013-11-06 15:23 ` Peter Zijlstra 2013-11-06 14:44 ` Peter Zijlstra 2013-11-06 16:07 ` Peter Zijlstra 2013-11-06 17:31 ` Vince Weaver 2013-11-06 18:24 ` Peter Zijlstra 2013-11-07 8:21 ` Ingo Molnar 2013-11-07 14:27 ` Vince Weaver 2013-11-07 15:55 ` Ingo Molnar 2013-11-11 16:24 ` Peter Zijlstra 2013-11-11 21:10 ` Ingo Molnar 2013-10-29 21:23 ` perf events ring buffer memory barrier on powerpc Michael Neuling 2013-10-29 21:23 ` Michael Neuling 2013-10-30 9:27 ` Paul E. McKenney 2013-10-30 9:27 ` Paul E. McKenney 2013-10-30 11:25 ` Peter Zijlstra 2013-10-30 11:25 ` Peter Zijlstra 2013-10-30 14:52 ` Victor Kaplansky 2013-10-30 14:52 ` Victor Kaplansky 2013-10-30 15:39 ` Peter Zijlstra 2013-10-30 15:39 ` Peter Zijlstra 2013-10-30 17:14 ` Victor Kaplansky 2013-10-30 17:14 ` Victor Kaplansky 2013-10-30 17:44 ` Peter Zijlstra 2013-10-30 17:44 ` Peter Zijlstra 2013-10-31 6:16 ` Paul E. McKenney 2013-10-31 6:16 ` Paul E. McKenney 2013-11-01 13:12 ` Victor Kaplansky 2013-11-01 13:12 ` Victor Kaplansky 2013-11-02 16:36 ` Paul E. McKenney 2013-11-02 16:36 ` Paul E. McKenney 2013-11-02 17:26 ` Paul E. McKenney 2013-11-02 17:26 ` Paul E. McKenney 2013-10-31 6:40 ` Paul E. McKenney 2013-10-31 6:40 ` Paul E. McKenney 2013-11-01 14:25 ` Victor Kaplansky 2013-11-01 14:25 ` Victor Kaplansky 2013-11-02 17:28 ` Paul E. McKenney 2013-11-02 17:28 ` Paul E. McKenney 2013-11-01 14:56 ` Peter Zijlstra 2013-11-01 14:56 ` Peter Zijlstra 2013-11-02 17:32 ` Paul E. McKenney 2013-11-02 17:32 ` Paul E. McKenney 2013-11-03 14:40 ` Paul E. McKenney 2013-11-03 14:40 ` Paul E. McKenney 2013-11-03 15:17 ` [RFC] arch: Introduce new TSO memory barrier smp_tmb() Peter Zijlstra 2013-11-03 15:17 ` Peter Zijlstra 2013-11-03 18:08 ` Linus Torvalds 2013-11-03 18:08 ` Linus Torvalds 2013-11-03 20:01 ` Peter Zijlstra 2013-11-03 20:01 ` Peter Zijlstra 2013-11-03 22:42 ` Paul E. McKenney 2013-11-03 22:42 ` Paul E. McKenney 2013-11-03 23:34 ` Linus Torvalds 2013-11-03 23:34 ` Linus Torvalds 2013-11-04 10:51 ` Paul E. McKenney 2013-11-04 10:51 ` Paul E. McKenney 2013-11-04 11:22 ` Peter Zijlstra 2013-11-04 11:22 ` Peter Zijlstra 2013-11-04 16:27 ` Paul E. McKenney 2013-11-04 16:27 ` Paul E. McKenney 2013-11-04 16:48 ` Peter Zijlstra 2013-11-04 16:48 ` Peter Zijlstra 2013-11-04 19:11 ` Peter Zijlstra 2013-11-04 19:11 ` Peter Zijlstra 2013-11-04 19:18 ` Peter Zijlstra 2013-11-04 19:18 ` Peter Zijlstra 2013-11-04 20:54 ` Paul E. McKenney 2013-11-04 20:54 ` Paul E. McKenney 2013-11-04 20:53 ` Paul E. McKenney 2013-11-04 20:53 ` Paul E. McKenney 2013-11-05 14:05 ` Will Deacon 2013-11-05 14:05 ` Will Deacon 2013-11-05 14:49 ` Paul E. McKenney 2013-11-05 14:49 ` Paul E. McKenney 2013-11-05 18:49 ` Peter Zijlstra 2013-11-05 18:49 ` Peter Zijlstra 2013-11-06 11:00 ` Will Deacon [this message] 2013-11-06 11:00 ` Will Deacon 2013-11-06 12:39 ` Peter Zijlstra 2013-11-06 12:39 ` Peter Zijlstra 2013-11-06 12:51 ` Geert Uytterhoeven 2013-11-06 12:51 ` Geert Uytterhoeven 2013-11-06 13:57 ` Peter Zijlstra 2013-11-06 13:57 ` Peter Zijlstra 2013-11-06 18:48 ` Paul E. McKenney 2013-11-06 18:48 ` Paul E. McKenney 2013-11-06 19:42 ` Peter Zijlstra 2013-11-06 19:42 ` Peter Zijlstra 2013-11-07 11:17 ` Will Deacon 2013-11-07 11:17 ` Will Deacon 2013-11-07 13:36 ` Peter Zijlstra 2013-11-07 13:36 ` Peter Zijlstra 2013-11-07 23:50 ` Mathieu Desnoyers 2013-11-07 23:50 ` Mathieu Desnoyers 2013-11-04 11:05 ` Will Deacon 2013-11-04 11:05 ` Will Deacon 2013-11-04 16:34 ` Paul E. McKenney 2013-11-04 16:34 ` Paul E. McKenney 2013-11-03 20:59 ` Benjamin Herrenschmidt 2013-11-03 20:59 ` Benjamin Herrenschmidt 2013-11-03 22:43 ` Paul E. McKenney 2013-11-03 22:43 ` Paul E. McKenney 2013-11-03 17:07 ` perf events ring buffer memory barrier on powerpc Will Deacon 2013-11-03 22:47 ` Paul E. McKenney 2013-11-04 9:57 ` Will Deacon 2013-11-04 10:52 ` Paul E. McKenney 2013-11-01 16:11 ` Peter Zijlstra 2013-11-01 16:11 ` Peter Zijlstra 2013-11-02 17:46 ` Paul E. McKenney 2013-11-02 17:46 ` Paul E. McKenney 2013-11-01 16:18 ` Peter Zijlstra 2013-11-01 16:18 ` Peter Zijlstra 2013-11-02 17:49 ` Paul E. McKenney 2013-11-02 17:49 ` Paul E. McKenney 2013-10-30 13:28 ` Victor Kaplansky 2013-10-30 13:28 ` Victor Kaplansky 2013-10-30 15:51 ` Peter Zijlstra 2013-10-30 15:51 ` Peter Zijlstra 2013-10-30 18:29 ` Peter Zijlstra 2013-10-30 18:29 ` Peter Zijlstra 2013-10-30 19:11 ` Peter Zijlstra 2013-10-30 19:11 ` Peter Zijlstra 2013-10-31 4:33 ` Paul E. McKenney 2013-10-31 4:33 ` Paul E. McKenney 2013-10-31 4:32 ` Paul E. McKenney 2013-10-31 4:32 ` Paul E. McKenney 2013-10-31 9:04 ` Peter Zijlstra 2013-10-31 9:04 ` Peter Zijlstra 2013-10-31 15:07 ` Paul E. McKenney 2013-10-31 15:07 ` Paul E. McKenney 2013-10-31 15:19 ` Peter Zijlstra 2013-10-31 15:19 ` Peter Zijlstra 2013-11-01 9:28 ` Paul E. McKenney 2013-11-01 9:28 ` Paul E. McKenney 2013-11-01 10:30 ` Peter Zijlstra 2013-11-01 10:30 ` Peter Zijlstra 2013-11-02 15:20 ` Paul E. McKenney 2013-11-02 15:20 ` Paul E. McKenney 2013-11-04 9:07 ` Peter Zijlstra 2013-11-04 9:07 ` Peter Zijlstra 2013-11-04 10:00 ` Paul E. McKenney 2013-11-04 10:00 ` Paul E. McKenney 2013-10-31 9:59 ` Victor Kaplansky 2013-10-31 9:59 ` Victor Kaplansky 2013-10-31 12:28 ` David Laight 2013-10-31 12:28 ` David Laight 2013-10-31 12:55 ` Victor Kaplansky 2013-10-31 12:55 ` Victor Kaplansky 2013-10-31 15:25 ` Paul E. McKenney 2013-10-31 15:25 ` Paul E. McKenney 2013-11-01 16:06 ` Victor Kaplansky 2013-11-01 16:06 ` Victor Kaplansky 2013-11-01 16:25 ` David Laight 2013-11-01 16:25 ` David Laight 2013-11-01 16:30 ` Victor Kaplansky 2013-11-01 16:30 ` Victor Kaplansky 2013-11-03 20:57 ` Benjamin Herrenschmidt 2013-11-03 20:57 ` Benjamin Herrenschmidt 2013-11-02 15:46 ` Paul E. McKenney 2013-11-02 15:46 ` Paul E. McKenney 2013-10-28 19:09 ` Oleg Nesterov 2013-10-28 19:09 ` Oleg Nesterov 2013-10-29 14:06 ` [tip:perf/urgent] perf: Fix perf ring buffer memory ordering tip-bot for Peter Zijlstra
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