Date: Tue, 7 Jul 2015 12:25:07 +0200
From: Pavel Machek <pavel@ucw.cz>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Alan Stern <stern@rowland.harvard.edu>, Dave Chinner <david@fromorbit.com>,
        Len Brown <lenb@kernel.org>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Linux PM list <linux-pm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Len Brown <len.brown@intel.com>
Subject: Re: [PATCH 1/1] suspend: delete sys_sync()
Message-ID: <20150707102507.GA13811@amd>
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On Mon 2015-07-06 15:59:15, Rafael J. Wysocki wrote:
> On Monday, July 06, 2015 01:06:45 PM Pavel Machek wrote:
> > On Mon 2015-07-06 01:28:20, Rafael J. Wysocki wrote:
> > > On Saturday, July 04, 2015 10:19:55 AM Alan Stern wrote:
> > > > On Sat, 4 Jul 2015, Rafael J. Wysocki wrote:
> > > > 
> > > > > The only argument against dropping sys_sync() from the suspend code path
> > > > > I've seen in this thread that I entirely agree with is that it may lead to
> > > > > regressions, because we've done it practically forever and it may hide latent
> > > > > bugs somewhere in block drivers etc.  Dropping it, though, is the only way
> > > > > to see those bugs, if any, and if we want to ever fix them, we need to see
> > > > > them.  That's why I think that it may be a good idea to allow people to
> > > > > drop it if they are willing to accept some extra risk (via the kernel
> > > > > command line, for example).
> > > > 
> > > > I'd be perfectly happy to have the sync selectable at runtime, one way 
> > > > or another.  The three most reasonable options seem to be:
> > > > 
> > > > 	kernel command line
> > > > 
> > > > 	sysfs file
> > > > 
> > > > 	sysctl setting
> > > > 
> > > > The command line is less flexible (it can't be changed after booting).  
> > > > Either of the other two would be fine with me.
> > > 
> > > We'll probably use a sysfs file (possibly plus a Kconfig option to set the
> > > boot time default).
> > 
> > Android people can already do sync-less s2ram using existing
> > interface. IMO they should just do it.
> > 
> > In any case, sysfs file + Kconfig is an overkill. We already have too
> > many Kconfig options.
> 
> I don't think we can reach a general agreement on what's the *right* approach
> with respect to the sys_sync() in the suspend code path, so the only way out
> of this situation I can see is to make it configurable.

So first: not having general agreement does not mean we should
introduce Kconfig + sysfs file. Second: your proposal of "lets sync if
runtime was shorter than xxx" is over complex, but at least should not
need Kconfig support... Third: we have ioctl() based interface, and I
guess android should use that one; it already has "s2ram without sync"
method.

> > There's not a single Android phone supported by mainline
> > kernel. I'm sure they have bigger problems than Android setting
> > default sysfs values...
> 
> But perhaps we'd like to change that?

We'd like to, but lets start with the real hard stuff (merging support
for Qualcomm chipsets) that is 1000000 LoC+, not with trivial tweaks
that would be 1-line change, but we pollute code with Kconfig+sysfs
making it 100..

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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