Messages in this thread Patch in this message | | | Date | Wed, 30 Aug 2017 17:25:42 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH v2] membarrier: provide register sync core cmd |
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----- On Aug 30, 2017, at 12:01 AM, Boqun Feng boqun.feng@gmail.com wrote:
> Hi Mathieu, > > On Sun, Aug 27, 2017 at 01:50:35PM -0700, Mathieu Desnoyers wrote: >> Add a new MEMBARRIER_CMD_REGISTER_SYNC_CORE command to the membarrier >> system call. It allows processes to register their intent to have their >> threads issue core serializing barriers in addition to memory barriers >> whenever a membarrier command is performed. >> >> It is relevant for reclaim of JIT code, which requires to issue core >> serializing barriers on all threads running on behalf of a process >> after ensuring the old code is not visible anymore, before re-using >> memory for new code. >> >> When a processes returns from a MEMBARRIER_CMD_REGISTER_SYNC_CORE >> command, it is guaranteed that all following MEMBARRIER_CMD_SHARED and >> MEMBARRIER_CMD_PRIVATE_EXPEDITED issue core serializing barriers, in >> addition to the memory barriers, on all of its running threads. >> >> * Scheduler Overhead Benchmarks >> >> Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz >> taskset 01 ./perf bench sched pipe -T >> Linux v4.13-rc6 >> >> Avg. usecs/op Std.Dev. usecs/op >> Before this change: 2.75 0.12 >> Non-registered processes: 2.73 0.08 >> Registered processes: 3.07 0.02 >> >> Changes since v1: >> - Add missing MEMBARRIER_CMD_REGISTER_SYNC_CORE header documentation, >> - Add benchmarks to commit message. >> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> >> CC: Peter Zijlstra <peterz@infradead.org> >> CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com> >> CC: Boqun Feng <boqun.feng@gmail.com> >> CC: Andrew Hunter <ahh@google.com> >> CC: Maged Michael <maged.michael@gmail.com> >> CC: gromer@google.com >> CC: Avi Kivity <avi@scylladb.com> >> CC: Benjamin Herrenschmidt <benh@kernel.crashing.org> >> CC: Paul Mackerras <paulus@samba.org> >> CC: Michael Ellerman <mpe@ellerman.id.au> >> CC: Dave Watson <davejwatson@fb.com> >> CC: Andy Lutomirski <luto@kernel.org> >> CC: Will Deacon <will.deacon@arm.com> >> CC: Hans Boehm <hboehm@google.com> >> --- >> fs/exec.c | 1 + >> include/linux/sched.h | 52 +++++++++++++++++++++++++++++++++++++++++ >> include/uapi/linux/membarrier.h | 8 +++++++ >> kernel/fork.c | 2 ++ >> kernel/sched/core.c | 3 +++ >> kernel/sched/membarrier.c | 37 ++++++++++++++++++++++++++--- >> 6 files changed, 100 insertions(+), 3 deletions(-) >> >> diff --git a/fs/exec.c b/fs/exec.c >> index 62175cbcc801..a4ab3253bac7 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -1794,6 +1794,7 @@ static int do_execveat_common(int fd, struct filename >> *filename, >> /* execve succeeded */ >> current->fs->in_exec = 0; >> current->in_execve = 0; >> + membarrier_execve(current); >> acct_update_integrals(current); >> task_numa_free(current); >> free_bprm(bprm); >> diff --git a/include/linux/sched.h b/include/linux/sched.h >> index 8337e2db0bb2..b1ecdc4e8b84 100644 >> --- a/include/linux/sched.h >> +++ b/include/linux/sched.h >> @@ -1086,6 +1086,9 @@ struct task_struct { >> /* Used by LSM modules for access restriction: */ >> void *security; >> #endif >> +#ifdef CONFIG_MEMBARRIER >> + int membarrier_sync_core; > > Why put this in task_struct rather than mm_struct? If the reclaim of JIT > code is one of the target users, don't you want to make this as a > attribute of an address space? > > Am I missing something subtle here?
Placing this in the task struct rather than in the mm struct saves a pointer dereference on scheduler fast-paths (task_struct *)->mm.
Thanks,
Mathieu
> > Regards, > Boqun > >> +#endif >> >> /* >> * New fields for task_struct should be added above here, so that >> @@ -1623,4 +1626,53 @@ extern long sched_getaffinity(pid_t pid, struct cpumask >> *mask); >> #define TASK_SIZE_OF(tsk) TASK_SIZE >> #endif >> >> +#ifdef CONFIG_MEMBARRIER >> +static inline void membarrier_fork(struct task_struct *t, >> + unsigned long clone_flags) >> +{ >> + /* >> + * Coherence of membarrier_sync_core against thread fork is >> + * protected by siglock. membarrier_fork is called with siglock >> + * held. >> + */ >> + t->membarrier_sync_core = current->membarrier_sync_core; >> +} >> +static inline void membarrier_execve(struct task_struct *t) >> +{ >> + t->membarrier_sync_core = 0; >> +} >> +static inline void membarrier_sched_out(struct task_struct *t) >> +{ >> + /* >> + * Core serialization is performed before the memory barrier >> + * preceding the store to rq->curr. >> + */ >> + if (unlikely(READ_ONCE(t->membarrier_sync_core))) >> + sync_core(); >> +} >> +static inline void membarrier_sched_in(struct task_struct *t) >> +{ >> + /* >> + * Core serialization is performed after the memory barrier >> + * following the store to rq->curr. >> + */ >> + if (unlikely(READ_ONCE(t->membarrier_sync_core))) >> + sync_core(); >> +} >> +#else >> +static inline void membarrier_fork(struct task_struct *t, >> + unsigned long clone_flags) >> +{ >> +} >> +static inline void membarrier_execve(struct task_struct *t) >> +{ >> +} >> +static inline void membarrier_sched_out(struct task_struct *t) >> +{ >> +} >> +static inline void membarrier_sched_in(struct task_struct *t) >> +{ >> +} >> +#endif >> + >> #endif >> diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h >> index 6d47b3249d8a..933c35ebcc10 100644 >> --- a/include/uapi/linux/membarrier.h >> +++ b/include/uapi/linux/membarrier.h >> @@ -56,6 +56,13 @@ >> * complete faster than the non-expedited ones, >> * they never block, but have the downside of >> * causing extra overhead. >> + * @MEMBARRIER_CMD_REGISTER_SYNC_CORE: >> + * Register the caller process so all of its >> + * threads will issue core serialization >> + * barriers in addition to memory barriers upon >> + * SHARED and PRIVATE barriers targeting >> + * its threads issued after this registration >> + * returns. >> * >> * Command to be passed to the membarrier system call. The commands need to >> * be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to >> @@ -67,6 +74,7 @@ enum membarrier_cmd { >> /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */ >> /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */ >> MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3), >> + MEMBARRIER_CMD_REGISTER_SYNC_CORE = (1 << 4), >> }; >> >> #endif /* _UAPI_LINUX_MEMBARRIER_H */ >> diff --git a/kernel/fork.c b/kernel/fork.c >> index 17921b0390b4..713b3c932671 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -1840,6 +1840,8 @@ static __latent_entropy struct task_struct *copy_process( >> */ >> copy_seccomp(p); >> >> + membarrier_fork(p, clone_flags); >> + >> /* >> * Process group and session signals need to be delivered to just the >> * parent before the fork or both the parent and the child after the >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 0e36d9960d91..3ca27d066950 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -3292,6 +3292,8 @@ static void __sched notrace __schedule(bool preempt) >> local_irq_disable(); >> rcu_note_context_switch(preempt); >> >> + membarrier_sched_out(prev); >> + >> /* >> * Make sure that signal_pending_state()->signal_pending() below >> * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE) >> @@ -3364,6 +3366,7 @@ static void __sched notrace __schedule(bool preempt) >> >> /* Also unlocks the rq: */ >> rq = context_switch(rq, prev, next, &rf); >> + membarrier_sched_in(next); >> } else { >> rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP); >> rq_unlock_irq(rq, &rf); >> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c >> index 7eec6914d2d2..f128caf64b49 100644 >> --- a/kernel/sched/membarrier.c >> +++ b/kernel/sched/membarrier.c >> @@ -25,12 +25,16 @@ >> * Bitmask made from a "or" of all commands within enum membarrier_cmd, >> * except MEMBARRIER_CMD_QUERY. >> */ >> -#define MEMBARRIER_CMD_BITMASK \ >> - (MEMBARRIER_CMD_SHARED | MEMBARRIER_CMD_PRIVATE_EXPEDITED) >> +#define MEMBARRIER_CMD_BITMASK \ >> + (MEMBARRIER_CMD_SHARED \ >> + | MEMBARRIER_CMD_PRIVATE_EXPEDITED \ >> + | MEMBARRIER_CMD_REGISTER_SYNC_CORE) >> >> static void ipi_mb(void *info) >> { >> - smp_mb(); /* IPIs should be serializing but paranoid. */ >> + /* IPIs should be serializing but paranoid. */ >> + smp_mb(); >> + sync_core(); >> } >> >> static void membarrier_private_expedited(void) >> @@ -96,6 +100,30 @@ static void membarrier_private_expedited(void) >> smp_mb(); /* exit from system call is not a mb */ >> } >> >> +static void membarrier_register_sync_core(void) >> +{ >> + struct task_struct *p = current, *t; >> + >> + if (get_nr_threads(p) == 1) { >> + p->membarrier_sync_core = 1; >> + return; >> + } >> + >> + /* >> + * Coherence of membarrier_sync_core against thread fork is >> + * protected by siglock. >> + */ >> + spin_lock(&p->sighand->siglock); >> + for_each_thread(p, t) >> + WRITE_ONCE(t->membarrier_sync_core, 1); >> + spin_unlock(&p->sighand->siglock); >> + /* >> + * Ensure all future scheduler execution will observe the new >> + * membarrier_sync_core state for this process. >> + */ >> + synchronize_sched(); >> +} >> + >> /** >> * sys_membarrier - issue memory barriers on a set of threads >> * @cmd: Takes command values defined in enum membarrier_cmd. >> @@ -146,6 +174,9 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) >> case MEMBARRIER_CMD_PRIVATE_EXPEDITED: >> membarrier_private_expedited(); >> return 0; >> + case MEMBARRIER_CMD_REGISTER_SYNC_CORE: >> + membarrier_register_sync_core(); >> + return 0; >> default: >> return -EINVAL; >> } >> -- >> 2.11.0
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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