linux-kernel - Re: [PATCH REBASED 3/6] s390: Add __down_read

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Date:   Sat, 30 Sep 2017 12:39:46 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, linux-ia64@...r.kernel.org,
        avagin@...tuozzo.com, peterz@...radead.org, hpa@...or.com,
        gorcunov@...tuozzo.com, linux-arch@...r.kernel.org,
        linux-s390@...r.kernel.org, x86@...nel.org, mingo@...hat.com,
        mattst88@...il.com, fenghua.yu@...el.com, arnd@...db.de,
        ink@...assic.park.msu.ru, tglx@...utronix.de, rth@...ddle.net,
        tony.luck@...el.com, linux-kernel@...r.kernel.org,
        linux-alpha@...r.kernel.org, davem@...emloft.net,
        rientjes@...gle.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH REBASED 3/6] s390: Add __down_read_killable()

On Sat, 30 Sep 2017 12:36:12 +0200
Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> On Sat, 30 Sep 2017 11:20:02 +0200
> Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> 
> > On Fri, Sep 29, 2017 at 07:06:18PM +0300, Kirill Tkhai wrote:  
> > > Similar to __down_write_killable(), and read killable primitive.
> > > 
> > > Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> > > ---
> > >  arch/s390/include/asm/rwsem.h |   18 ++++++++++++++++--
> > >  1 file changed, 16 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/s390/include/asm/rwsem.h b/arch/s390/include/asm/rwsem.h    
> > 
> > FWIW, while looking into this patch I realized that we never optimized our
> > rwsem primitives to make use of new atomic instructions.
> > 
> > The generic rwsem header file however does, since it uses atomic ops which
> > we did optimize. Even when compiling for old machines the generic version
> > generates better code. Therefore I will remove the 15 years old s390
> > implementation and switch to the generic version instead.  
> 
> Take care not to conflict with the queued spinlock/rwlock patches on the
> features branch. 
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=eb3b7b848fb3dd00f7a57d633d4ae4d194aa7865
> 
> Me thinks that what you have in mind is already done.

Argh, pitfall rwlock != rwsem. Using the atomic_ops for the rwsem code makes
a lot of sense. Yes, please..

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.