linux-kernel - Re: [patch 1/4] spinlock: lockbreak cleanup

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Message-ID: <20071101155347.GB745@wotan.suse.de>
Date:	Thu, 1 Nov 2007 16:53:47 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, riel <riel@...hat.com>
Subject: Re: [patch 1/4] spinlock: lockbreak cleanup

On Thu, Nov 01, 2007 at 04:46:36PM +0100, Ingo Molnar wrote:
> 
> * Lee Schermerhorn <Lee.Schermerhorn@...com> wrote:
> 
> > > I guess it was done to make the "template" hacks eaiser. I don't 
> > > really find that in good taste, especially for important core 
> > > infrastructure. Anyway.
> > 
> > Actually, what I had/have is a cond_resched_rwlock() that I needed to 
> > convert the i_mmap_lock() to rw for testing reclaim scalability.  
> > [I've seen a large system running an Oracle OLTP load hang spitting 
> > "cpu soft lockup" messages with all cpus spinning on a i_mmap_lock 
> > spin lock.] One of the i_mmap_lock paths uses cond_resched_lock() for 
> > spin locks. To do a straight forward conversion [and maybe that isn't 
> > the right approach], I created the cond_resched_rwlock() function by 
> > generalizing the cond_sched_lock() code and creating both spin and rw 
> > lock wrappers. I took advantage of the fact that, currently, 
> > need_lockbreak() is a macro and that both spin and rw locks have/had 
> > the break_lock member. Typesafe functions would probably be 
> > preferrable, if we want to keep break_lock for rw spin locks.
> > 
> > Here's the most recent posting:
> > 
> > 	http://marc.info/?l=linux-mm&m=118980356306014&w=4
> > 
> > See the changes to sched.[ch].  Should apply to 23-mm1 with offsets 
> > and minor fixup in fs/inode.c.
> 
> yep. I'm too in favor of keeping the need-lockbreak mechanism and its 
> type-insensitive data structure. We've got way too many locking 
> primitives and keeping them all sorted is nontrivial already.

I think a large contributor to that is being a bit clever with indirections
and cute code (eg. like this template stuff), rather than having two types of
spinlocks instead of one.


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