linux-kernel - Re: [PATCH 03/10] locking/rwsem: Rename kernel/locking/rwsem.h

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Message-ID: <20190213155423.GZ32494@hirez.programming.kicks-ass.net>
Date:   Wed, 13 Feb 2019 16:54:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH 03/10] locking/rwsem: Rename kernel/locking/rwsem.h

On Wed, Feb 13, 2019 at 10:47:11AM -0500, Waiman Long wrote:
> On 02/13/2019 04:19 AM, Peter Zijlstra wrote:
> > On Tue, Feb 12, 2019 at 07:27:00PM -0500, Waiman Long wrote:
> >> The content of kernel/locking/rwsem.h is now specific to rwsem-xadd only.
> >> Rename it to rwsem-xadd.h to indicate that it is specific to rwsem-xadd
> >> and include it only when CONFIG_RWSEM_XCHGADD_ALGORITHM is set. As a result,
> >> the CONFIG_RWSEM_XCHGADD_ALGORITHM conditional compilation directives can
> >> be removed. There is no functional change.
> > Since all of rwsem-xadd is now generic code; how about we delete the
> > spinlock thing and keep everything rwsem ?
> >
> > We don't carry a special spinlock mutex implementation either. And
> > arguably any arch that uses spinlock based atomics (afaict the only case
> > where rwsem-spinlock makes any sense anyway) suck anyway.
> 
> I don't mind removing the rwsem-spinlock code and have just one
> implementation for all as long as there is no objection from others. I
> don't know the history of why we have 2 implementations of rwsem and so
> I didn't plan to do that.

It is from before my time too; but I think rwsem-spinlock is generic and
didn't require arch asm helpers, where rwsem-xadd did, but we just fixed
that :-)