linux-kernel - Re: [PATCH 1/1] suspend: delete sys

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Date:	Sat, 4 Jul 2015 10:19:55 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Dave Chinner <david@...morbit.com>, Len Brown <lenb@...nel.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 1/1] suspend: delete sys_sync()

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.

> Moreover, question is if we really need to carry out the sync on *every*
> suspend even if it is not pointless overall.  That shouldn't really be
> necessary if we suspend and resume often enough or if we resume only for
> a while and then suspend again.  Maybe it should be rate limited somehow
> at least?

For example, skip the sync if the system has been awake for < 100 ms?  
The cutoff time could also be controlled by the sysfs file: -1 =>
never sync, 0 => always sync, > 0 => sync if the system has been awake 
longer than the value.

Alan Stern

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