| Message ID | 20240110145533.60234-3-parri.andrea@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | membarrier: riscv: Core serializing command | expand |
Hi, On 1/10/24 06:55, Andrea Parri wrote: > To gather the architecture requirements of the "private/global > expedited" membarrier commands. The file will be expanded to > integrate further information about the membarrier syscall (as > needed/desired in the future). While at it, amend some related > inline comments in the membarrier codebase. > > Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Signed-off-by: Andrea Parri <parri.andrea@gmail.com> > --- > Documentation/scheduler/index.rst | 1 + > Documentation/scheduler/membarrier.rst | 37 ++++++++++++++++++++++++++ > MAINTAINERS | 1 + > kernel/sched/core.c | 7 ++++- > kernel/sched/membarrier.c | 8 +++--- > 5 files changed, 49 insertions(+), 5 deletions(-) > create mode 100644 Documentation/scheduler/membarrier.rst > > diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst > index 3170747226f6d..43bd8a145b7a9 100644 > --- a/Documentation/scheduler/index.rst > +++ b/Documentation/scheduler/index.rst > @@ -7,6 +7,7 @@ Scheduler > > > completion > + membarrier > sched-arch > sched-bwc > sched-deadline > diff --git a/Documentation/scheduler/membarrier.rst b/Documentation/scheduler/membarrier.rst > new file mode 100644 > index 0000000000000..ab7ee3824b407 > --- /dev/null > +++ b/Documentation/scheduler/membarrier.rst > @@ -0,0 +1,37 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +======================== > +membarrier() System Call > +======================== > + > +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements > +===================================================================== > + > +Memory barriers before updating rq->curr > +---------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +coming from user-space, before updating rq->curr. This barrier is implied > +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The > +barrier matches a full barrier in the proximity of the membarrier system > +call exit, cf. membarrier_{private,global}_expedited(). > + What does "The command" refer to above and below, please? Thanks. > +Memory barriers after updating rq->curr > +--------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +updating rq->curr, before returning to user-space. The schemes providing > +this barrier on the various architectures are as follows. > + > + - alpha, arc, arm, hexagon, mips rely on the full barrier implied by > + spin_unlock() in finish_lock_switch(). > + > + - arm64 relies on the full barrier implied by switch_to(). > + > + - powerpc, riscv, s390, sparc, x86 rely on the full barrier implied by > + switch_mm(), if mm is not NULL; they rely on the full barrier implied > + by mmdrop(), otherwise. On powerpc and riscv, switch_mm() relies on > + membarrier_arch_switch_mm(). > + > +The barrier matches a full barrier in the proximity of the membarrier system > +call entry, cf. membarrier_{private,global}_expedited().
Hi Randy, > > +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements > > +===================================================================== > > + > > +Memory barriers before updating rq->curr > > +---------------------------------------- > > + > > +The command requires each architecture to have a full memory barrier after > > +coming from user-space, before updating rq->curr. This barrier is implied > > +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The > > +barrier matches a full barrier in the proximity of the membarrier system > > +call exit, cf. membarrier_{private,global}_expedited(). > > + > > What does "The command" refer to above and below, please? The term was meant to refer to any of MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDITED (from the section title); FWIW, this seems to align with the terminology adopted in MEMBARRIER(2) for example. Mmh, unless I get a better idea, I'll expand those occurrences to: "The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDIDED require [...]" Andrea
On 1/10/24 11:05, Andrea Parri wrote: > Hi Randy, > >>> +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements >>> +===================================================================== >>> + >>> +Memory barriers before updating rq->curr >>> +---------------------------------------- >>> + >>> +The command requires each architecture to have a full memory barrier after >>> +coming from user-space, before updating rq->curr. This barrier is implied >>> +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The >>> +barrier matches a full barrier in the proximity of the membarrier system >>> +call exit, cf. membarrier_{private,global}_expedited(). >>> + >> >> What does "The command" refer to above and below, please? > > The term was meant to refer to any of MEMBARRIER_CMD_PRIVATE_EXPEDITED and > MEMBARRIER_CMD_GLOBAL_EXPEDITED (from the section title); FWIW, this seems > to align with the terminology adopted in MEMBARRIER(2) for example. I see. > Mmh, unless I get a better idea, I'll expand those occurrences to: > > "The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDIDED > require [...]" _EXPEDITED OK, that's better IMO. Thanks.
> > Mmh, unless I get a better idea, I'll expand those occurrences to: > > > > "The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDIDED > > require [...]" > _EXPEDITED Oops. :-| Thanks. Andrea
On 2024-01-10 09:55, Andrea Parri wrote: > To gather the architecture requirements of the "private/global > expedited" membarrier commands. The file will be expanded to > integrate further information about the membarrier syscall (as > needed/desired in the future). While at it, amend some related > inline comments in the membarrier codebase. Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Signed-off-by: Andrea Parri <parri.andrea@gmail.com> > --- > Documentation/scheduler/index.rst | 1 + > Documentation/scheduler/membarrier.rst | 37 ++++++++++++++++++++++++++ > MAINTAINERS | 1 + > kernel/sched/core.c | 7 ++++- > kernel/sched/membarrier.c | 8 +++--- > 5 files changed, 49 insertions(+), 5 deletions(-) > create mode 100644 Documentation/scheduler/membarrier.rst > > diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst > index 3170747226f6d..43bd8a145b7a9 100644 > --- a/Documentation/scheduler/index.rst > +++ b/Documentation/scheduler/index.rst > @@ -7,6 +7,7 @@ Scheduler > > > completion > + membarrier > sched-arch > sched-bwc > sched-deadline > diff --git a/Documentation/scheduler/membarrier.rst b/Documentation/scheduler/membarrier.rst > new file mode 100644 > index 0000000000000..ab7ee3824b407 > --- /dev/null > +++ b/Documentation/scheduler/membarrier.rst > @@ -0,0 +1,37 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +======================== > +membarrier() System Call > +======================== > + > +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements > +===================================================================== > + > +Memory barriers before updating rq->curr > +---------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +coming from user-space, before updating rq->curr. This barrier is implied > +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The > +barrier matches a full barrier in the proximity of the membarrier system > +call exit, cf. membarrier_{private,global}_expedited(). > + > +Memory barriers after updating rq->curr > +--------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +updating rq->curr, before returning to user-space. The schemes providing > +this barrier on the various architectures are as follows. > + > + - alpha, arc, arm, hexagon, mips rely on the full barrier implied by > + spin_unlock() in finish_lock_switch(). > + > + - arm64 relies on the full barrier implied by switch_to(). > + > + - powerpc, riscv, s390, sparc, x86 rely on the full barrier implied by > + switch_mm(), if mm is not NULL; they rely on the full barrier implied > + by mmdrop(), otherwise. On powerpc and riscv, switch_mm() relies on > + membarrier_arch_switch_mm(). > + > +The barrier matches a full barrier in the proximity of the membarrier system > +call entry, cf. membarrier_{private,global}_expedited(). > diff --git a/MAINTAINERS b/MAINTAINERS > index 0f8cec504b2ba..6bce0aeecb4f2 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -13815,6 +13815,7 @@ M: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > M: "Paul E. McKenney" <paulmck@kernel.org> > L: linux-kernel@vger.kernel.org > S: Supported > +F: Documentation/scheduler/membarrier.rst > F: arch/*/include/asm/membarrier.h > F: include/uapi/linux/membarrier.h > F: kernel/sched/membarrier.c > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 711dc753f7216..b51bc86f8340c 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6599,7 +6599,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) > * if (signal_pending_state()) if (p->state & @state) > * > * Also, the membarrier system call requires a full memory barrier > - * after coming from user-space, before storing to rq->curr. > + * after coming from user-space, before storing to rq->curr; this > + * barrier matches a full barrier in the proximity of the membarrier > + * system call exit. > */ > rq_lock(rq, &rf); > smp_mb__after_spinlock(); > @@ -6677,6 +6679,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) > * architectures where spin_unlock is a full barrier, > * - switch_to() for arm64 (weakly-ordered, spin_unlock > * is a RELEASE barrier), > + * > + * The barrier matches a full barrier in the proximity of > + * the membarrier system call entry. > */ > ++*switch_count; > > diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c > index 2ad881d07752c..f3d91628d6b8a 100644 > --- a/kernel/sched/membarrier.c > +++ b/kernel/sched/membarrier.c > @@ -251,7 +251,7 @@ static int membarrier_global_expedited(void) > return 0; > > /* > - * Matches memory barriers around rq->curr modification in > + * Matches memory barriers after rq->curr modification in > * scheduler. > */ > smp_mb(); /* system call entry is not a mb. */ > @@ -300,7 +300,7 @@ static int membarrier_global_expedited(void) > > /* > * Memory barrier on the caller thread _after_ we finished > - * waiting for the last IPI. Matches memory barriers around > + * waiting for the last IPI. Matches memory barriers before > * rq->curr modification in scheduler. > */ > smp_mb(); /* exit from system call is not a mb */ > @@ -339,7 +339,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) > return 0; > > /* > - * Matches memory barriers around rq->curr modification in > + * Matches memory barriers after rq->curr modification in > * scheduler. > */ > smp_mb(); /* system call entry is not a mb. */ > @@ -415,7 +415,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) > > /* > * Memory barrier on the caller thread _after_ we finished > - * waiting for the last IPI. Matches memory barriers around > + * waiting for the last IPI. Matches memory barriers before > * rq->curr modification in scheduler. > */ > smp_mb(); /* exit from system call is not a mb */
diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst index 3170747226f6d..43bd8a145b7a9 100644 --- a/Documentation/scheduler/index.rst +++ b/Documentation/scheduler/index.rst @@ -7,6 +7,7 @@ Scheduler completion + membarrier sched-arch sched-bwc sched-deadline diff --git a/Documentation/scheduler/membarrier.rst b/Documentation/scheduler/membarrier.rst new file mode 100644 index 0000000000000..ab7ee3824b407 --- /dev/null +++ b/Documentation/scheduler/membarrier.rst @@ -0,0 +1,37 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================== +membarrier() System Call +======================== + +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements +===================================================================== + +Memory barriers before updating rq->curr +---------------------------------------- + +The command requires each architecture to have a full memory barrier after +coming from user-space, before updating rq->curr. This barrier is implied +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The +barrier matches a full barrier in the proximity of the membarrier system +call exit, cf. membarrier_{private,global}_expedited(). + +Memory barriers after updating rq->curr +--------------------------------------- + +The command requires each architecture to have a full memory barrier after +updating rq->curr, before returning to user-space. The schemes providing +this barrier on the various architectures are as follows. + + - alpha, arc, arm, hexagon, mips rely on the full barrier implied by + spin_unlock() in finish_lock_switch(). + + - arm64 relies on the full barrier implied by switch_to(). + + - powerpc, riscv, s390, sparc, x86 rely on the full barrier implied by + switch_mm(), if mm is not NULL; they rely on the full barrier implied + by mmdrop(), otherwise. On powerpc and riscv, switch_mm() relies on + membarrier_arch_switch_mm(). + +The barrier matches a full barrier in the proximity of the membarrier system +call entry, cf. membarrier_{private,global}_expedited(). diff --git a/MAINTAINERS b/MAINTAINERS index 0f8cec504b2ba..6bce0aeecb4f2 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13815,6 +13815,7 @@ M: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> M: "Paul E. McKenney" <paulmck@kernel.org> L: linux-kernel@vger.kernel.org S: Supported +F: Documentation/scheduler/membarrier.rst F: arch/*/include/asm/membarrier.h F: include/uapi/linux/membarrier.h F: kernel/sched/membarrier.c diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 711dc753f7216..b51bc86f8340c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6599,7 +6599,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) * if (signal_pending_state()) if (p->state & @state) * * Also, the membarrier system call requires a full memory barrier - * after coming from user-space, before storing to rq->curr. + * after coming from user-space, before storing to rq->curr; this + * barrier matches a full barrier in the proximity of the membarrier + * system call exit. */ rq_lock(rq, &rf); smp_mb__after_spinlock(); @@ -6677,6 +6679,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) * architectures where spin_unlock is a full barrier, * - switch_to() for arm64 (weakly-ordered, spin_unlock * is a RELEASE barrier), + * + * The barrier matches a full barrier in the proximity of + * the membarrier system call entry. */ ++*switch_count; diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 2ad881d07752c..f3d91628d6b8a 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -251,7 +251,7 @@ static int membarrier_global_expedited(void) return 0; /* - * Matches memory barriers around rq->curr modification in + * Matches memory barriers after rq->curr modification in * scheduler. */ smp_mb(); /* system call entry is not a mb. */ @@ -300,7 +300,7 @@ static int membarrier_global_expedited(void) /* * Memory barrier on the caller thread _after_ we finished - * waiting for the last IPI. Matches memory barriers around + * waiting for the last IPI. Matches memory barriers before * rq->curr modification in scheduler. */ smp_mb(); /* exit from system call is not a mb */ @@ -339,7 +339,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) return 0; /* - * Matches memory barriers around rq->curr modification in + * Matches memory barriers after rq->curr modification in * scheduler. */ smp_mb(); /* system call entry is not a mb. */ @@ -415,7 +415,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) /* * Memory barrier on the caller thread _after_ we finished - * waiting for the last IPI. Matches memory barriers around + * waiting for the last IPI. Matches memory barriers before * rq->curr modification in scheduler. */ smp_mb(); /* exit from system call is not a mb */
To gather the architecture requirements of the "private/global expedited" membarrier commands. The file will be expanded to integrate further information about the membarrier syscall (as needed/desired in the future). While at it, amend some related inline comments in the membarrier codebase. Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> --- Documentation/scheduler/index.rst | 1 + Documentation/scheduler/membarrier.rst | 37 ++++++++++++++++++++++++++ MAINTAINERS | 1 + kernel/sched/core.c | 7 ++++- kernel/sched/membarrier.c | 8 +++--- 5 files changed, 49 insertions(+), 5 deletions(-) create mode 100644 Documentation/scheduler/membarrier.rst