include/linux/rcupdate.h | 2 +- include/linux/rcutree.h | 2 +- include/linux/srcutiny.h | 2 +- kernel/rcu/Kconfig | 4 ++-- kernel/rcu/srcutiny.c | 14 +++++++------- kernel/rcu/tree_plugin.h | 22 +++++++++++++++++----- kernel/sched/core.c | 4 +++- kernel/trace/trace_osnoise.c | 32 +++++++++++++++----------------- 8 files changed, 47 insertions(+), 35 deletions(-)
This series adds RCU bits for lazy preemption.
The problem addressed is that pre-PREEMPT_LAZY, PREEMPTION=y implied
PREEMPT_RCU=y. With PREEMPT_LAZY, that's no longer true.
That's because PREEMPT_RCU makes some trade-offs to optimize for
latency as opposed to throughput, and configurations with limited
preemption might prefer the stronger forward-progress guarantees of
PREEMPT_RCU=n.
Accordingly, with standalone PREEMPT_LAZY (much like PREEMPT_NONE,
PREEMPT_VOLUNTARY) we want to use PREEMPT_RCU=n. And, when used in
conjunction with PREEMPT_DYNAMIC, we continue to use PREEMPT_RCU=y.
Patches 1-3 are cleanup patches:
"rcu: fix header guard for rcu_all_qs()"
"rcu: rename PREEMPT_AUTO to PREEMPT_LAZY"
"sched: update __cond_resched comment about RCU quiescent states"
Patch 4,
"rcu: handle unstable rdp in rcu_read_unlock_strict()"
handles a latent RCU bug rcu_report_qs_rdp() could be called with
an unstable rdp.
Patches 5 and 6,
"rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y"
"osnoise: provide quiescent states"
handle quiescent states for the (PREEMPT_LAZY=y, PREEMPT_RCU=n)
configuration.
And, finally patch 7, "rcu: limit PREEMPT_RCU configurations",
explicitly limits PREEMPT_RCU=y to the PREEMPT_DYNAMIC or the latency
oriented models.
Changelog:
v3:
- moved patch-3 to be the last one in the series (suggested by Sebastian)
- added "rcu: handle unstable rdp in rcu_read_unlock_strict()"
(suggested by Frederic Weisbecker).
- switched to a more robust check in rcu_flavor_sched_clock_irq()
(suggested by Frederic Weisbecker).
- simplified check in osnoise (suggested by Frederic Weisbecker).
- dropped an unrelated scheduler patch.
v2:
- fixup incorrect usage of tif_need_resched_lazy() (comment from
from Sebastian Andrzej Siewior)
- massaged the commit messages a bit
- drops the powerpc support for PREEMPT_LAZY as that was orthogonal
to this series (Shrikanth will send that out separately.)
Please review.
Ankur Arora (7):
rcu: fix header guard for rcu_all_qs()
rcu: rename PREEMPT_AUTO to PREEMPT_LAZY
sched: update __cond_resched comment about RCU quiescent states
rcu: handle unstable rdp in rcu_read_unlock_strict()
rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
osnoise: provide quiescent states
rcu: limit PREEMPT_RCU configurations
include/linux/rcupdate.h | 2 +-
include/linux/rcutree.h | 2 +-
include/linux/srcutiny.h | 2 +-
kernel/rcu/Kconfig | 4 ++--
kernel/rcu/srcutiny.c | 14 +++++++-------
kernel/rcu/tree_plugin.h | 22 +++++++++++++++++-----
kernel/sched/core.c | 4 +++-
kernel/trace/trace_osnoise.c | 32 +++++++++++++++-----------------
8 files changed, 47 insertions(+), 35 deletions(-)
--
2.43.5
On Thu, Dec 12, 2024 at 08:06:51PM -0800, Ankur Arora wrote: > This series adds RCU bits for lazy preemption. > > The problem addressed is that pre-PREEMPT_LAZY, PREEMPTION=y implied > PREEMPT_RCU=y. With PREEMPT_LAZY, that's no longer true. > > That's because PREEMPT_RCU makes some trade-offs to optimize for > latency as opposed to throughput, and configurations with limited > preemption might prefer the stronger forward-progress guarantees of > PREEMPT_RCU=n. > > Accordingly, with standalone PREEMPT_LAZY (much like PREEMPT_NONE, > PREEMPT_VOLUNTARY) we want to use PREEMPT_RCU=n. And, when used in > conjunction with PREEMPT_DYNAMIC, we continue to use PREEMPT_RCU=y. > > Patches 1-3 are cleanup patches: > "rcu: fix header guard for rcu_all_qs()" > "rcu: rename PREEMPT_AUTO to PREEMPT_LAZY" > "sched: update __cond_resched comment about RCU quiescent states" > > Patch 4, > "rcu: handle unstable rdp in rcu_read_unlock_strict()" > > handles a latent RCU bug rcu_report_qs_rdp() could be called with > an unstable rdp. > > Patches 5 and 6, > "rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y" > "osnoise: provide quiescent states" > > handle quiescent states for the (PREEMPT_LAZY=y, PREEMPT_RCU=n) > configuration. > > And, finally patch 7, "rcu: limit PREEMPT_RCU configurations", > explicitly limits PREEMPT_RCU=y to the PREEMPT_DYNAMIC or the latency > oriented models. Pulled into my -rcu tree for further review and testing, with initial tests passing. Apologies for the delay! Thanx, Paul > Changelog: > > v3: > - moved patch-3 to be the last one in the series (suggested by Sebastian) > - added "rcu: handle unstable rdp in rcu_read_unlock_strict()" > (suggested by Frederic Weisbecker). > - switched to a more robust check in rcu_flavor_sched_clock_irq() > (suggested by Frederic Weisbecker). > - simplified check in osnoise (suggested by Frederic Weisbecker). > - dropped an unrelated scheduler patch. > > v2: > - fixup incorrect usage of tif_need_resched_lazy() (comment from > from Sebastian Andrzej Siewior) > - massaged the commit messages a bit > - drops the powerpc support for PREEMPT_LAZY as that was orthogonal > to this series (Shrikanth will send that out separately.) > > Please review. > > Ankur Arora (7): > rcu: fix header guard for rcu_all_qs() > rcu: rename PREEMPT_AUTO to PREEMPT_LAZY > sched: update __cond_resched comment about RCU quiescent states > rcu: handle unstable rdp in rcu_read_unlock_strict() > rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y > osnoise: provide quiescent states > rcu: limit PREEMPT_RCU configurations > > include/linux/rcupdate.h | 2 +- > include/linux/rcutree.h | 2 +- > include/linux/srcutiny.h | 2 +- > kernel/rcu/Kconfig | 4 ++-- > kernel/rcu/srcutiny.c | 14 +++++++------- > kernel/rcu/tree_plugin.h | 22 +++++++++++++++++----- > kernel/sched/core.c | 4 +++- > kernel/trace/trace_osnoise.c | 32 +++++++++++++++----------------- > 8 files changed, 47 insertions(+), 35 deletions(-) > > -- > 2.43.5 >
Paul E. McKenney <paulmck@kernel.org> writes: > On Thu, Dec 12, 2024 at 08:06:51PM -0800, Ankur Arora wrote: >> This series adds RCU bits for lazy preemption. >> >> The problem addressed is that pre-PREEMPT_LAZY, PREEMPTION=y implied >> PREEMPT_RCU=y. With PREEMPT_LAZY, that's no longer true. >> >> That's because PREEMPT_RCU makes some trade-offs to optimize for >> latency as opposed to throughput, and configurations with limited >> preemption might prefer the stronger forward-progress guarantees of >> PREEMPT_RCU=n. >> >> Accordingly, with standalone PREEMPT_LAZY (much like PREEMPT_NONE, >> PREEMPT_VOLUNTARY) we want to use PREEMPT_RCU=n. And, when used in >> conjunction with PREEMPT_DYNAMIC, we continue to use PREEMPT_RCU=y. >> >> Patches 1-3 are cleanup patches: >> "rcu: fix header guard for rcu_all_qs()" >> "rcu: rename PREEMPT_AUTO to PREEMPT_LAZY" >> "sched: update __cond_resched comment about RCU quiescent states" >> >> Patch 4, >> "rcu: handle unstable rdp in rcu_read_unlock_strict()" >> >> handles a latent RCU bug rcu_report_qs_rdp() could be called with >> an unstable rdp. >> >> Patches 5 and 6, >> "rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y" >> "osnoise: provide quiescent states" >> >> handle quiescent states for the (PREEMPT_LAZY=y, PREEMPT_RCU=n) >> configuration. >> >> And, finally patch 7, "rcu: limit PREEMPT_RCU configurations", >> explicitly limits PREEMPT_RCU=y to the PREEMPT_DYNAMIC or the latency >> oriented models. > > Pulled into my -rcu tree for further review and testing, with initial > tests passing. Apologies for the delay! Great. Thanks Paul! Ankur >> Changelog: >> >> v3: >> - moved patch-3 to be the last one in the series (suggested by Sebastian) >> - added "rcu: handle unstable rdp in rcu_read_unlock_strict()" >> (suggested by Frederic Weisbecker). >> - switched to a more robust check in rcu_flavor_sched_clock_irq() >> (suggested by Frederic Weisbecker). >> - simplified check in osnoise (suggested by Frederic Weisbecker). >> - dropped an unrelated scheduler patch. >> >> v2: >> - fixup incorrect usage of tif_need_resched_lazy() (comment from >> from Sebastian Andrzej Siewior) >> - massaged the commit messages a bit >> - drops the powerpc support for PREEMPT_LAZY as that was orthogonal >> to this series (Shrikanth will send that out separately.) >> >> Please review. >> >> Ankur Arora (7): >> rcu: fix header guard for rcu_all_qs() >> rcu: rename PREEMPT_AUTO to PREEMPT_LAZY >> sched: update __cond_resched comment about RCU quiescent states >> rcu: handle unstable rdp in rcu_read_unlock_strict() >> rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y >> osnoise: provide quiescent states >> rcu: limit PREEMPT_RCU configurations >> >> include/linux/rcupdate.h | 2 +- >> include/linux/rcutree.h | 2 +- >> include/linux/srcutiny.h | 2 +- >> kernel/rcu/Kconfig | 4 ++-- >> kernel/rcu/srcutiny.c | 14 +++++++------- >> kernel/rcu/tree_plugin.h | 22 +++++++++++++++++----- >> kernel/sched/core.c | 4 +++- >> kernel/trace/trace_osnoise.c | 32 +++++++++++++++----------------- >> 8 files changed, 47 insertions(+), 35 deletions(-) >> >> -- >> 2.43.5 >> -- ankur
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