Messages in this thread | | | Date | Wed, 24 Jan 2024 11:13:16 -0500 | Subject | Re: [PATCH v3 2/4] membarrier: Create Documentation/scheduler/membarrier.rst | From | Mathieu Desnoyers <> |
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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 */
-- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
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