Re: [PATCH] bpf: local_storage: avoid redundant IRQ save on bucket locks

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

+Cc Amery

On Wed Sep 16, 2026 at 8:10 PM CEST, Usama Arif wrote:
> bpf_local_storage_update() takes the map bucket lock while holding
> local_storage->lock. bpf_selem_unlink_map() does the same; its only
> caller holds local_storage->lock. The outer lock is acquired with
> raw_res_spin_lock_irqsave(), so interrupts are already disabled at both
> sites.
>
> Using raw_res_spin_lock_irqsave() for the nested lock saves the already
> disabled IRQ state and issues another IRQ disable. The matching unlock
> tests that saved state before leaving interrupts disabled. On x86-64,
> this adds a pushfq/popq/cli sequence and a test/branch around an
> unreachable sti to each acquisition.
>
> Use raw_res_spin_lock() and raw_res_spin_unlock() instead. They retain
> preemption nesting, memory ordering and resilient-lock bookkeeping. The
> outer unlock remains responsible for restoring the caller's IRQ state.
>
> In the tested clang x86-64 build, this removes five executed instructions
> from each uncontended nested acquisition. It also shrinks
> bpf_local_storage_update() from 1732 to 1702 bytes and bpf_selem_unlink()
> from 1030 to 992 bytes. The affected paths are updates that add or replace
> an element in existing owner storage and successful unlinks.
>
> Document the owner-lock requirement of bpf_selem_unlink_map() and assert
> that interrupts are disabled.
>
> Signed-off-by: Usama Arif <usama.arif@linux.dev>
> ---

Makes sense. But did you observe any measurable improvement with this change?

> [...]