Messages in this thread | | | Subject | Re: [PATCH v2 tip/core/rcu 4/6] srcu: Provide polling interfaces for Tiny SRCU grace periods | From | Neeraj Upadhyay <> | Date | Wed, 25 Nov 2020 10:09:22 +0530 |
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On 11/25/2020 1:00 AM, Paul E. McKenney wrote: > On Tue, Nov 24, 2020 at 10:44:24AM +0530, Neeraj Upadhyay wrote: >> >> >> On 11/24/2020 2:42 AM, Paul E. McKenney wrote: >>> On Mon, Nov 23, 2020 at 10:13:13AM +0530, Neeraj Upadhyay wrote: >>>> >>>> >>>> On 11/21/2020 6:29 AM, paulmck@kernel.org wrote: >>>>> From: "Paul E. McKenney" <paulmck@kernel.org> >>>>> >>>>> There is a need for a polling interface for SRCU grace >>>>> periods, so this commit supplies get_state_synchronize_srcu(), >>>>> start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this >>>>> purpose. The first can be used if future grace periods are inevitable >>>>> (perhaps due to a later call_srcu() invocation), the second if future >>>>> grace periods might not otherwise happen, and the third to check if a >>>>> grace period has elapsed since the corresponding call to either of the >>>>> first two. >>>>> >>>>> As with get_state_synchronize_rcu() and cond_synchronize_rcu(), >>>>> the return value from either get_state_synchronize_srcu() or >>>>> start_poll_synchronize_srcu() must be passed in to a later call to >>>>> poll_state_synchronize_srcu(). >>>>> >>>>> Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ >>>>> Reported-by: Kent Overstreet <kent.overstreet@gmail.com> >>>>> [ paulmck: Add EXPORT_SYMBOL_GPL() per kernel test robot feedback. ] >>>>> [ paulmck: Apply feedback from Neeraj Upadhyay. ] >>>>> Link: https://lore.kernel.org/lkml/20201117004017.GA7444@paulmck-ThinkPad-P72/ >>>>> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> >>>>> --- >>>>> include/linux/rcupdate.h | 2 ++ >>>>> include/linux/srcu.h | 3 +++ >>>>> include/linux/srcutiny.h | 1 + >>>>> kernel/rcu/srcutiny.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++-- >>>>> 4 files changed, 56 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h >>>>> index de08264..e09c0d8 100644 >>>>> --- a/include/linux/rcupdate.h >>>>> +++ b/include/linux/rcupdate.h >>>>> @@ -33,6 +33,8 @@ >>>>> #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) >>>>> #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) >>>>> #define ulong2long(a) (*(long *)(&(a))) >>>>> +#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) >>>>> +#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) >>>>> /* Exported common interfaces */ >>>>> void call_rcu(struct rcu_head *head, rcu_callback_t func); >>>>> diff --git a/include/linux/srcu.h b/include/linux/srcu.h >>>>> index e432cc9..a0895bb 100644 >>>>> --- a/include/linux/srcu.h >>>>> +++ b/include/linux/srcu.h >>>>> @@ -60,6 +60,9 @@ void cleanup_srcu_struct(struct srcu_struct *ssp); >>>>> int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); >>>>> void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp); >>>>> void synchronize_srcu(struct srcu_struct *ssp); >>>>> +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp); >>>>> +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp); >>>>> +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie); >>>>> #ifdef CONFIG_DEBUG_LOCK_ALLOC >>>>> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h >>>>> index d9edb67..c7f0c1f 100644 >>>>> --- a/include/linux/srcutiny.h >>>>> +++ b/include/linux/srcutiny.h >>>>> @@ -16,6 +16,7 @@ >>>>> struct srcu_struct { >>>>> short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */ >>>>> unsigned short srcu_idx; /* Current reader array element in bit 0x2. */ >>>>> + unsigned short srcu_idx_max; /* Furthest future srcu_idx request. */ >>>>> u8 srcu_gp_running; /* GP workqueue running? */ >>>>> u8 srcu_gp_waiting; /* GP waiting for readers? */ >>>>> struct swait_queue_head srcu_wq; >>>>> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c >>>>> index 3bac1db..b073175 100644 >>>>> --- a/kernel/rcu/srcutiny.c >>>>> +++ b/kernel/rcu/srcutiny.c >>>>> @@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) >>>>> ssp->srcu_gp_running = false; >>>>> ssp->srcu_gp_waiting = false; >>>>> ssp->srcu_idx = 0; >>>>> + ssp->srcu_idx_max = 0; >>>>> INIT_WORK(&ssp->srcu_work, srcu_drive_gp); >>>>> INIT_LIST_HEAD(&ssp->srcu_work.entry); >>>>> return 0; >>>> >>>> Minor: cleanup_srcu_struct() can probably have 2 new sanity checks? >>>> >>>> WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); >>>> WARN_ON(ssp->srcu_idx & 1); >>> >>> Good point, added and under test. >>> >>>> Thanks >>>> Neeraj >>>> >>>>> @@ -114,7 +115,7 @@ void srcu_drive_gp(struct work_struct *wp) >>>>> struct srcu_struct *ssp; >>>>> ssp = container_of(wp, struct srcu_struct, srcu_work); >>>>> - if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head)) >>>>> + if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) >>>>> return; /* Already running or nothing to do. */ >>>>> /* Remove recently arrived callbacks and wait for readers. */ >>>>> @@ -147,13 +148,18 @@ void srcu_drive_gp(struct work_struct *wp) >>>>> * straighten that out. >>>>> */ >>>>> WRITE_ONCE(ssp->srcu_gp_running, false); >>>>> - if (READ_ONCE(ssp->srcu_cb_head)) >>>>> + if (USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) >>>>> schedule_work(&ssp->srcu_work); >>>>> } >>>>> EXPORT_SYMBOL_GPL(srcu_drive_gp); >>>>> static void srcu_gp_start_if_needed(struct srcu_struct *ssp) >>>>> { >>>>> + unsigned short cookie; >>>>> + >>>>> + cookie = get_state_synchronize_srcu(ssp); >>>>> + if (USHORT_CMP_LT(READ_ONCE(ssp->srcu_idx_max), cookie)) >>>>> + WRITE_ONCE(ssp->srcu_idx_max, cookie); >>>> >>>> Minor: Maybe we can return in the else part of USHORT_CMP_LT check, to avoid >>>> scheduling work? >>> >>> How about like this? >> >> Looks good! > > Are you willing to give an ack or reviewed-by for either patch? > > Thanx, Paul >
For the version in rcu -dev
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Thanks Neeraj
>> Thanks >> Neeraj >> >>> >>> static void srcu_gp_start_if_needed(struct srcu_struct *ssp) >>> { >>> unsigned short cookie; >>> >>> cookie = get_state_synchronize_srcu(ssp); >>> if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) >>> return; >>> WRITE_ONCE(ssp->srcu_idx_max, cookie); >>> if (!READ_ONCE(ssp->srcu_gp_running)) { >>> if (likely(srcu_init_done)) >>> schedule_work(&ssp->srcu_work); >>> else if (list_empty(&ssp->srcu_work.entry)) >>> list_add(&ssp->srcu_work.entry, &srcu_boot_list); >>> } >>> } >>> >>> Testing this next. ;-) >>> >>> Thanx, Paul >>> >>>> Thanks >>>> Neeraj >>>> >>>>> if (!READ_ONCE(ssp->srcu_gp_running)) { >>>>> if (likely(srcu_init_done)) >>>>> schedule_work(&ssp->srcu_work); >>>>> @@ -196,6 +202,48 @@ void synchronize_srcu(struct srcu_struct *ssp) >>>>> } >>>>> EXPORT_SYMBOL_GPL(synchronize_srcu); >>>>> +/* >>>>> + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie >>>>> + */ >>>>> +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) >>>>> +{ >>>>> + unsigned long ret; >>>>> + >>>>> + barrier(); >>>>> + ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; >>>>> + barrier(); >>>>> + return ret & USHRT_MAX; >>>>> +} >>>>> +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); >>>>> + >>>>> +/* >>>>> + * start_poll_synchronize_srcu - Provide cookie and start grace period >>>>> + * >>>>> + * The difference between this and get_state_synchronize_srcu() is that >>>>> + * this function ensures that the poll_state_synchronize_srcu() will >>>>> + * eventually return the value true. >>>>> + */ >>>>> +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) >>>>> +{ >>>>> + unsigned long ret = get_state_synchronize_srcu(ssp); >>>>> + >>>>> + srcu_gp_start_if_needed(ssp); >>>>> + return ret; >>>>> +} >>>>> +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); >>>>> + >>>>> +/* >>>>> + * poll_state_synchronize_srcu - Has cookie's grace period ended? >>>>> + */ >>>>> +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) >>>>> +{ >>>>> + bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie); >>>>> + >>>>> + barrier(); >>>>> + return ret; >>>>> +} >>>>> +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); >>>>> + >>>>> /* Lockdep diagnostics. */ >>>>> void __init rcu_scheduler_starting(void) >>>>> { >>>>> >>>> >>>> -- >>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of >>>> the Code Aurora Forum, hosted by The Linux Foundation >> >> -- >> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of >> the Code Aurora Forum, hosted by The Linux Foundation
-- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
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