linux-kernel - Re: sem_lock() vs qspinlocks

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Message-ID: <20160520090034.GO3205@twins.programming.kicks-ass.net>
Date:	Fri, 20 May 2016 11:00:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	manfred@...orfullife.com, Waiman.Long@....com, mingo@...nel.org,
	torvalds@...ux-foundation.org, ggherdovich@...e.com,
	mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: sem_lock() vs qspinlocks

On Fri, May 20, 2016 at 10:30:08AM +0200, Peter Zijlstra wrote:
> On Thu, May 19, 2016 at 10:39:26PM -0700, Davidlohr Bueso wrote:
> > Specifically
> > for the 'cascade_cond' and 'cascade_flock' programs, which exhibit hangs in libc's
> > semop() blocked waiting for zero.
> 
> OK; so I've been running:
> 
> while :; do
>   bin/cascade_cond -E -C 200 -L -S -W -T 200  -I 2000000 ;
>   bin/cascade_flock -E -C 200 -L -S -W -P 200 -I 5000000 ;
> done
> 
> for a few minutes now and its not stuck and my machine didn't splat.
> 
> Am I not doing it right?

Hooray, it went *bang*.. OK, lemme have a harder look at this semaphore
code.