Hi Paul, On Wed, Nov 05, 2025 at 12:32:15PM -0800, Paul E. McKenney wrote: > Some arm64 platforms have slow per-CPU atomic operations, for example, > the Neoverse V2. This commit therefore moves SRCU-fast from per-CPU > atomic operations to interrupt-disabled non-read-modify-write-atomic > atomic_read()/atomic_set() operations. This works because > SRCU-fast-updown is not invoked from read-side primitives, which > means that if srcu_read_unlock_fast() NMI handlers. This means that > srcu_read_lock_fast_updown() and srcu_read_unlock_fast_updown() can > exclude themselves and each other > > This reduces the overhead of calls to srcu_read_lock_fast_updown() and > srcu_read_unlock_fast_updown() from about 100ns to about 12ns on an ARM > Neoverse V2. Although this is not excellent compared to about 2ns on x86, > it sure beats 100ns. > > This command was used to measure the overhead: > > tools/testing/selftests/rcutorture/bin/kvm.sh --torture refscale --allcpus > --duration 5 --configs NOPREEMPT --kconfig "CONFIG_NR_CPUS=64 > CONFIG_TASKS_TRACE_RCU=y" --bootargs "refscale.loops=100000 > refscale.guest_os_delay=5 refscale.nreaders=64 refscale.holdoff=30 > torture.disable_onoff_at_boot refscale.scale_type=srcu-fast-updown > refscale.verbose_batched=8 torture.verbose_sleep_frequency=8 > torture.verbose_sleep_duration=8 refscale.nruns=100" --trust-make > > Signed-off-by: Paul E. McKenney <[email protected]> > Cc: Catalin Marinas <[email protected]> > Cc: Will Deacon <[email protected]> > Cc: Mark Rutland <[email protected]> > Cc: Mathieu Desnoyers <[email protected]> > Cc: Steven Rostedt <[email protected]> > Cc: Sebastian Andrzej Siewior <[email protected]> > Cc: <[email protected]> > Cc: <[email protected]> > --- > include/linux/srcutree.h | 51 +++++++++++++++++++++++++++++++++++++--- > 1 file changed, 48 insertions(+), 3 deletions(-)
I've queued the per-cpu tweak from Catalin in the arm64 fixes tree [1] for 6.18, so please can you drop this SRCU commit from your tree? Cheers, Will [1] https://git.kernel.org/arm64/c/535fdfc5a228
