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

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Date:	Fri, 15 May 2015 11:35:57 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Ming Lei <tom.leiming@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Dave Chinner <david@...morbit.com>, NeilBrown <neilb@...e.de>,
	Len Brown <lenb@...nel.org>,
	Linux PM List <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 1/1] suspend: delete sys_sync()

> > Data loss may be caused for hotplug storage(like USB), or all storage
> > when power is exhausted during suspend.
> 
> Which also may very well happen at run time, right?

Intuitively users treat "suspended" as a bit like off and do remove
devices they've "finished with".

Technically yes the instant off/on on a phone is the same as the suspend
to RAM on a laptop but it doesn't mean the model in people's heads is the
same... not yet anyway.

> > Is there obvious advantage to remove sys_sync() in the case?
> 
> Yes, there is.  It is not necessary to sync() every time you suspend
> if you do that very often.

But if you do it very often you won't have any dirty pages to flush so it
will be very fast.

> And it is done in such a place that everything needs to wait for it to complete.

Only because the code deciding to trigger any automated suspend doesn't
do a sync a few seconds before. In the case the user goes to the menus
and does power->suspend then yes it's a delay. In the case where the OS
at some level has decided that it's 10 seconds from automatically
suspending to something the user space can issue a pre-emptive sync to
get the queue size down.

Alan
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