linux-kernel - Re: [PATCH] lglock: add read-preference local-global rwlock

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Message-ID: <20130302170145.GA29769@redhat.com>
Date:	Sat, 2 Mar 2013 18:01:45 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	paulmck@...ux.vnet.ibm.com,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Lai Jiangshan <eag0628@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	linux-doc@...r.kernel.org, peterz@...radead.org,
	fweisbec@...il.com, linux-kernel@...r.kernel.org,
	namhyung@...nel.org, mingo@...nel.org, linux-arch@...r.kernel.org,
	linux@....linux.org.uk, xiaoguangrong@...ux.vnet.ibm.com,
	wangyun@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	linux-pm@...r.kernel.org, rusty@...tcorp.com.au,
	rostedt@...dmis.org, rjw@...k.pl, vincent.guittot@...aro.org,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	netdev@...r.kernel.org, sbw@....edu, tj@...nel.org,
	akpm@...ux-foundation.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] lglock: add read-preference local-global rwlock

On 03/02, Lai Jiangshan wrote:
>
> On 02/03/13 02:28, Oleg Nesterov wrote:
> > Lai, I didn't read this discussion except the code posted by Michel.
> > I'll try to read this patch carefully later, but I'd like to ask
> > a couple of questions.
> >
> > This version looks more complex than Michel's, why? Just curious, I
> > am trying to understand what I missed. See
> > http://marc.info/?l=linux-kernel&m=136196350213593
>
> Michel changed my old draft version a little, his version is good enough for me.

Yes, I see. But imho Michel suggested the valuable cleanup, the code
becomes even more simple with the same perfomance.

Your v2 looks almost correct to me, but I still think it makes sense
to incorporate the simplification from Michel.

> My new version tries to add a little better nestable support with only
> adding single __this_cpu_op() in _read_[un]lock().

How? Afaics with or without FALLBACK_BASE you need _reed + _inc/dec in
_read_lock/unlock.

Oleg.

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