On 10/25/21 9:06 AM, Arnd Bergmann wrote:
On Mon, Oct 25, 2021 at 11:57 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxx> wrote:On 10/22/21 7:59 AM, Arnd Bergmann wrote: From: Arnd Bergmann <arnd@xxxxxxxx> 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@xxxxxxxx>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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