[PATCH v2 00/20] arm64: Preemptible this_cpu_*() operations

[David Laight]

On Wed, 2 Sep 2026 12:55:12 +0100
Usama Anjum <usama.anjum at arm.com> wrote:

> On 04/08/2026 6:04 pm, Mark Rutland wrote:
> > This series reworks arm64's this_cpu_*() operations such that they do
> > not need to disable preemption, avoiding related overhead in the fast
> > paths. Instead, the ops begin/end a "PCPU GPR" critical section using
> > unconditional/posted stores, which should be very cheap on any
> > reasonable micro-architecture. During a critical section, should a
> > (preemptible) exception be taken, the entry code will apply a fixup to
> > the GPRs containing the percpu offset and the generated percpu address.
...
> tl;dr
> Comparing this series with the page-table series [a] gives 8 improvements and 3
> regressions.
> 
> Fastpath is a Linux kernel performance benchmarking service. The table
> compares the both patched kernels: positive values are faster, negative
> values are slower, and (I)/(R) indicate statistically significant
> improvements/regressions. Unmarked differences are not significant after
> accounting for confidence and noise thresholds.
> 
> +---------------------------------+--------------------+-----------------+-----------------------+
> | Benchmark                       | percpu-pgtable [2] |   gpr-fixup [3] |         gpr-fixup [3] |
> |                                 |    vs baseline [1] | vs baseline [1] | vs percpu-pgtable [2] |
> +=================================+====================+=================+=======================+
...
> | perf/futex                      |              0.55% |      (R) -2.80% |            (R) -3.34% |
> | perf/sched                      |          (I) 1.61% |          -0.39% |            (R) -1.97% |

Might be worth investigating those two.
Something odd is probably happening.

David