From mboxrd@z Thu Jan  1 00:00:00 1970
From: Waiman Long <longman@redhat.com>
Date: Mon, 25 Oct 2021 18:25:32 +0000
Subject: Re: [PATCH] locking: remove spin_lock_flags() etc
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To: Arnd Bergmann <arnd@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>, Boqun Feng <boqun.feng@gmail.com>, Jonas Bonn <jonas@southpole.se>, Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>, Stafford Horne <shorne@gmail.com>, "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>, Helge Deller <deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Alexander Gordeev <agordeev@linux.ibm.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-ia64@vger.kernel.org, Openrisc <openrisc@lists.librecores.org>, Parisc List <linux-parisc@vger.kernel.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-s390 <linux-s390@vger.kernel.org>

On 10/25/21 11:44 AM, Arnd Bergmann wrote:
> On Mon, Oct 25, 2021 at 5:28 PM Waiman Long <longman@redhat.com> wrote:
>> On 10/25/21 9:06 AM, Arnd Bergmann wrote:
>>> 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.
> Sorry, I should not have said "normal" here. See arch/s390/lib/spinlock.c
> for their custom queued spinlocks as implemented in arch_spin_lock_queued().
> I don't know if that code actually does the same thing as the generic qspinlock,
> but it seems at least similar.

Yes, you are right. Their queued lock code looks like a custom version 
of the pvqspinlock code.

Cheers,
Longman