Messages in this thread | | | Subject | Re: [PATCH v2 tip/core/rcu 1/6] srcu: Make Tiny SRCU use multi-bit grace-period counter | From | Neeraj Upadhyay <> | Date | Tue, 24 Nov 2020 10:48:57 +0530 |
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On 11/24/2020 1:25 AM, Paul E. McKenney wrote: > On Mon, Nov 23, 2020 at 10:01:13AM +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. This >>> polling needs to distinguish between an SRCU instance being idle on the >>> one hand or in the middle of a grace period on the other. This commit >>> therefore converts the Tiny SRCU srcu_struct structure's srcu_idx from >>> a defacto boolean to a free-running counter, using the bottom bit to >>> indicate that a grace period is in progress. The second-from-bottom >>> bit is thus used as the index returned by srcu_read_lock(). >>> >>> Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ >>> Reported-by: Kent Overstreet <kent.overstreet@gmail.com> >>> [ paulmck: Fix __srcu_read_lock() idx computation Neeraj per Upadhyay. ] >>> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> >>> --- >>> include/linux/srcutiny.h | 4 ++-- >>> kernel/rcu/srcutiny.c | 5 +++-- >>> 2 files changed, 5 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h >>> index 5a5a194..d9edb67 100644 >>> --- a/include/linux/srcutiny.h >>> +++ b/include/linux/srcutiny.h >>> @@ -15,7 +15,7 @@ >>> struct srcu_struct { >>> short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */ >>> - short srcu_idx; /* Current reader array element. */ >>> + unsigned short srcu_idx; /* Current reader array element in bit 0x2. */ >>> u8 srcu_gp_running; /* GP workqueue running? */ >>> u8 srcu_gp_waiting; /* GP waiting for readers? */ >>> struct swait_queue_head srcu_wq; >>> @@ -59,7 +59,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp) >>> { >>> int idx; >>> - idx = READ_ONCE(ssp->srcu_idx); >>> + idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; >>> WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1); >>> return idx; >>> } >> >> Need change in idx calcultion in srcu_torture_stats_print() ? >> >> static inline void srcu_torture_stats_print(struct srcu_struct *ssp, >> idx = READ_ONCE(ssp->srcu_idx) & 0x1; > > Excellent point! It should match the calculation in __srcu_read_lock(), > shouldn't it? I have updated this, thank you! > > Thanx, Paul >
Updated version looks good!
Thanks Neeraj
>> Thanks >> Neeraj >> >>> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c >>> index 6208c1d..5598cf6 100644 >>> --- a/kernel/rcu/srcutiny.c >>> +++ b/kernel/rcu/srcutiny.c >>> @@ -124,11 +124,12 @@ void srcu_drive_gp(struct work_struct *wp) >>> ssp->srcu_cb_head = NULL; >>> ssp->srcu_cb_tail = &ssp->srcu_cb_head; >>> local_irq_enable(); >>> - idx = ssp->srcu_idx; >>> - WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx); >>> + idx = (ssp->srcu_idx & 0x2) / 2; >>> + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); >>> WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ >>> swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); >>> WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ >>> + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); >>> /* Invoke the callbacks we removed above. */ >>> while (lh) { >>> >> >> -- >> 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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