Messages in this thread | | | Subject | Re: [PATCH] locking: remove spin_lock_flags() etc | From | Waiman Long <> | Date | Mon, 25 Oct 2021 11:28:37 -0400 |
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On 10/25/21 9:06 AM, Arnd Bergmann wrote: > On Mon, Oct 25, 2021 at 11:57 AM Peter Zijlstra <peterz@infradead.org> wrote: >> On Sat, Oct 23, 2021 at 06:04:57PM +0200, Arnd Bergmann wrote: >>> On Sat, Oct 23, 2021 at 3:37 AM Waiman Long <longman@redhat.com> wrote: >>>>> On 10/22/21 7:59 AM, Arnd Bergmann wrote: >>>>> From: Arnd Bergmann <arnd@arndb.de> >>>>> >>>>> As this is all dead code, just remove it and the helper functions built >>>>> around it. For arch/ia64, the inline asm could be cleaned up, but >>>>> it seems safer to leave it untouched. >>>>> >>>>> Signed-off-by: Arnd Bergmann <arnd@arndb.de> >>>> Does that mean we can also remove the GENERIC_LOCKBREAK config option >>>> from the Kconfig files as well? >>> I couldn't figure this out. >>> >>> What I see is that the only architectures setting GENERIC_LOCKBREAK are >>> nds32, parisc, powerpc, s390, sh and sparc64, while the only architectures >>> implementing arch_spin_is_contended() are arm32, csky and ia64. >>> >>> The part I don't understand is whether the option actually does anything >>> useful any more after commit d89c70356acf ("locking/core: Remove break_lock >>> field when CONFIG_GENERIC_LOCKBREAK=y"). >> Urgh, what a mess.. AFAICT there's still code in >> kernel/locking/spinlock.c that relies on it. Specifically when >> GENERIC_LOCKBREAK=y we seem to create _lock*() variants that are >> basically TaS locks which drop preempt/irq disable while spinning. >> >> Anybody having this on and not having native TaS locks is in for a rude >> surprise I suppose... sparc64 being the obvious candidate there :/ > Is this a problem on s390 and powerpc, those two being the ones > that matter in practice? > > On s390, we pick between the cmpxchg() based directed-yield when > running on virtualized CPUs, and a normal qspinlock when running on a > dedicated CPU.
I am not aware that s390 is using qspinlocks at all as I don't see ARCH_USE_QUEUED_SPINLOCKS being set anywhere under arch/s390. I only see that it uses a cmpxchg based spinlock.
Cheers, Longman
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