linux-kernel - Re: [PATCH v2 0/9] Remove spin_unlock

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Message-Id: <20170708114112.GO2393@linux.vnet.ibm.com>
Date:   Sat, 8 Jul 2017 04:41:12 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...LAB.COM>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "manfred@...orfullife.com" <manfred@...orfullife.com>,
        "tj@...nel.org" <tj@...nel.org>, "arnd@...db.de" <arnd@...db.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 0/9] Remove spin_unlock_wait()

On Sat, Jul 08, 2017 at 10:43:24AM +0200, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Fri, Jul 07, 2017 at 10:31:28AM +0200, Ingo Molnar wrote:
> > 
> > [ . . . ]
> > 
> > > In fact I'd argue that any future high performance spin_unlock_wait() user is 
> > > probably better off open coding the unlock-wait poll loop (and possibly thinking 
> > > hard about eliminating it altogether). If such patterns pop up in the kernel we 
> > > can think about consolidating them into a single read-only primitive again.
> > 
> > I would like any reintroduction to include a header comment saying exactly
> > what the consolidated primitive actually does and does not do.  ;-)
> > 
> > > I.e. I think the proposed changes are doing no harm, and the unavailability of a 
> > > generic primitive does not hinder future optimizations either in any significant 
> > > fashion.
> > 
> > I will have a v3 with updated comments from Manfred.  Thoughts on when/where
> > to push this?
> 
> Once everyone agrees I can apply it to the locking tree. I think PeterZ's was the 
> only objection?

Oleg wasn't all that happy, either, but he did supply the relevant patch.

> > The reason I ask is if this does not go in during this merge window, I need
> > to fix the header comment on spin_unlock_wait().
> 
> Can try it next week after some testing - let's see how busy things get for Linus 
> in the merge window?

Sounds good!  Either way is fine with me.

							Thanx, Paul