linux-kernel - Re: [PATCH RFC] s390/sclp: pass timeout as HZ independent value

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Date:	Fri, 29 May 2015 11:51:54 +0200
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Nicholas Mc Guire <hofrat@...dl.org>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux390@...ibm.com, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] s390/sclp: pass timeout as HZ independent value

On Fri, 29 May 2015, Heiko Carstens wrote:

> On Wed, May 27, 2015 at 07:04:43PM +0200, Nicholas Mc Guire wrote:
> > schedule_timeout takes a timeout in jiffies but the code currently is
> > passing in a constant SDIAS_SLEEP_TICKS which sounds like it should be
> > in jiffies but it is actually not and thus makes this timeout HZ
> > dependent, to fix this it is passed through msecs_to_jiffies().
> > 
> > patch was not even compile tested as s390 toolchain from kernel.org 
> > failed for me (on a debian wheezy x86_64) with:
> > cc1: error: unrecognized command line option '-mtune=zEC12'
> > 
> > Patch is against 4.0-rc5 (localversion-next is -next-20150527)
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > ---
> > 
> > As there is no documentation of the intended timeout it might be wrong
> > to convert it with msecs_to_jiffies() since the effective timeout is 
> > at least a factor 10 smaller than it is now - so someone that knows this
> > driver needs to check on the actual value - but in any case it needs to
> > be passed in a HZ independent way.
> 
> Yes, the orginal code seems to be broken. Since I've no idea what the intended
> timeout value should be, let's simply ask Michael, who wrote this code eight
> years ago ;)
> While these lines get touched anyway, it would make sense to use
> schedule_timeout_interruptible() instead, and get rid of set_current_state().
>
Well that is not really equivalent
schedule_timeout_interruptible() is doing
__set_current_state not set_current_state
so that would drop the mb() and no WRITE_ONCE()

thx!
hofrat
 
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