From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Date: Mon, 25 Oct 2021 15:28:37 +0000 Subject: Re: [PATCH] locking: remove spin_lock_flags() etc Message-Id: <2413f412-a390-bbc0-e848-e2a77d1f0ab3@redhat.com> List-Id: References: <20211022120058.1031690-1-arnd@kernel.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Arnd Bergmann , Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Arnd Bergmann , Boqun Feng , Jonas Bonn , Stefan Kristiansson , Stafford Horne , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Alexander Gordeev , Linux Kernel Mailing List , linux-ia64@vger.kernel.org, Openrisc , Parisc List , linuxppc-dev , linux-s390 On 10/25/21 9:06 AM, Arnd Bergmann wrote: > On Mon, Oct 25, 2021 at 11:57 AM Peter Zijlstra 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 wrote: >>>>> On 10/22/21 7:59 AM, Arnd Bergmann wrote: >>>>> From: Arnd Bergmann >>>>> >>>>> 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 >>>> 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