linux-kernel - Re: [PATCH v4 2/3] locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs

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Date:   Thu, 14 Feb 2019 12:12:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Waiman Long <longman@...hat.com>, Christoph Hellwig <hch@....de>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        linux-mips@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-riscv@...ts.infradead.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-c6x-dev@...ux-c6x.org,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "moderated list:H8/300 ARCHITECTURE" 
        <uclinux-h8-devel@...ts.sourceforge.jp>,
        linux-xtensa@...ux-xtensa.org, Arnd Bergmann <arnd@...db.de>,
        linux-um@...ts.infradead.org,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Openrisc <openrisc@...ts.librecores.org>,
        Borislav Petkov <bp@...en8.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        nios2-dev@...ts.rocketboards.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v4 2/3] locking/rwsem: Remove rwsem-spinlock.c & use
 rwsem-xadd.c for all archs

On Thu, Feb 14, 2019 at 11:54:47AM +0100, Geert Uytterhoeven wrote:
> On Wed, Feb 13, 2019 at 11:01 PM Waiman Long <longman@...hat.com> wrote:
> > Currently, we have two different implementation of rwsem:
> >  1) CONFIG_RWSEM_GENERIC_SPINLOCK (rwsem-spinlock.c)
> >  2) CONFIG_RWSEM_XCHGADD_ALGORITHM (rwsem-xadd.c)
> >
> > As we are going to use a single generic implementation for rwsem-xadd.c
> > and no architecture-specific code will be needed, there is no point
> > in keeping two different implementations of rwsem. In most cases, the
> > performance of rwsem-spinlock.c will be worse. It also doesn't get all
> > the performance tuning and optimizations that had been implemented in
> > rwsem-xadd.c over the years.
> >
> > For simplication, we are going to remove rwsem-spinlock.c and make all
> > architectures use a single implementation of rwsem - rwsem-xadd.c.
> >
> > All references to RWSEM_GENERIC_SPINLOCK and RWSEM_XCHGADD_ALGORITHM
> > in the code are removed.
> >
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Waiman Long <longman@...hat.com>
> 
> Note that this conflicts with "[PATCH 03/11] kernel/locks: consolidate
> RWSEM_GENERIC_* options"
> https://lore.kernel.org/lkml/20190213174005.28785-4-hch@lst.de/

*sigh*.. of that never was Cc'ed to locking people :/