Re: [PATCH V7 4/5] asm-generic: spinlock: Add combo spinlock (ticket & queued)

Arnd Bergmann
2022-06-29T08:30:00Z

On Wed, Jun 29, 2022 at 10:24 AM Guo Ren <guoren@kernel.org> wrote:
> On Wed, Jun 29, 2022 at 3:09 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wed, Jun 29, 2022 at 3:34 AM Waiman Long <longman@redhat.com> wrote:
> >
> > From looking at the header file dependencies on arm64, I know that
> > putting jump labels into core infrastructure like the arch_spin_lock()
> > makes a big mess of indirect includes and measurably slows down
> > the kernel build.
> arm64 needn't combo spinlock, it could use pure qspinlock with keeping
> current header files included.

arm64 has a different problem: there are two separate sets of atomic
instructions, and the decision between those is similarly done using
jump labels. I definitely like the ability to choose between qspinlock
and ticket spinlock on arm64 as well. This can be done as a
compile-time choice, but both of them still depend on jump labels.

Arnd