Hi
On Tue, 2018-10-02 at 14:34 +0200, Hans de Goede wrote:
> On 02-10-18 14:26, Justin Forbes wrote:
> > On Tue, Oct 2, 2018 at 5:53 AM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > > Hi Justin,
> > >
> > > On 01-10-18 16:14, Justin Forbes wrote:
> > > > On Sun, Sep 30, 2018 at 1:52 PM, Hans de Goede <hdegoede@xxxxxxxxxx>
> > > > wrote:
> > > > > Hello Fedora kernel team,
> > > > >
> > > > > On the Fedora desktop list there has been a discussion about
> > > > > systemd now offering a new suspend-then-hibernate option and
> > > > > gnome-settings-daemon's media-keys plugin using this when
> > > > > the power-button gets pressed and systemd saying this is
> > > > > available on the system.
> > > > >
> > > > > What this does is suspend the system normally and set
> > > > > a RTC wakeup 3 hours in the future, then when the RTC wake
> > > > > happens it hibernates the system.
> > > > >
> > > > > As discussed on the desktop list this is not really desirable
> > > > > as default behavior for F29 (and later) since the hibernate
> > > > > code is not really something which gets used enough to be
> > > > > well tested and is really not something which we can support.
> > > > >
> > > > > So after that the discussion has gone in the direction of
> > > > > how to disable the new suspend-then-hibernate behavior.
> > > > >
> > > > > Lennart made a really interesting observation here, systemd
> > > > > is just proxying if "cat /sys/power/disk" indicates that
> > > > > hibernate is supported.
> > > > >
> > > >
> > > > No, that is not what systemd is doing. The kernel provides a
> > > > mechanism, it does absolutely nothing with that mechanism unless told
> > > > to do so. What systemd is actually doing is creating a policy around
> > > > that mechanism.
> > >
> > > systemd is really *not* creating policy here, it has a DBUS API
> > > call called CanHibernate which really just proxies what the kernel
> > > advertises.
> > >
> > > What is new is that GNOME (g-s-d) now uses it be default through
> > > by choosing suspend-then-hibernate as suspend action when
> > > hibernation is available.
> > >
> >
> > Right, so systemd really is just proxying, and Gnome is now creating a
> > policy. It does not change the underlying issue, we shouldn't cripple
> > a mechanism because someone wants to introduce a new undesirable
> > policy on top of it. Especially when the thing introducing that
> > policy is not the only user of the mechanism.
> >
> > > > > So if we really don't want to support hibernation as a normal
> > > > > option, while still allowing adventurous user to use it, what
> > > > > really should happen is for the kernel to stop advertising
> > > > > hibernate support. Thinking about this I agree, if we say
> > > > > that we cannot support it, the kernel really should not be
> > > > > advertising support for it by default.
> > > > >
> > > >
> > > > "We have decided that the policy created is not desirable, so we want
> > > > to disable the mechanism"
> > >
> > > Default to off is a different thing then disabling this.
> > >
> >
> > There is a difference between a "policy default to off", and "turning
> > off the mechanism". I would expect a new policy defaulting to off
> > would actually default to whatever is currently there. When a user
> > upgrades from F28 to F30, it seems wrong that their power
> > configuration would change in a way that is unexpected, and frankly
> > more difficult to manage. A regular user can run gnome-tweaks and
> > decide on lid behavior. A regular user cannot edit the kernel command
> > line once a system is booted. Now, it requires root. And we are
> > making it harder for people to edit it as a system boots with other
> > planned changes.
> >
> > > TBH I'm a bit surprised about your objections against this:
> > >
> > > 1) We all seem to agree that this is something which may or
> > > may not work, but is not something which we want to advertise
> > > as a "supported" Fedora feature
> > >
> > > 2) Given 1) we also all agree that we should not use it
> > > by default
> > >
> > > 3) If we should not use it by default then shouldn't the
> > > feature default to off ? That is all what is being suggested,
> > > basically the equivalent of adding "nohibernate" to the
> > > kernel commandline by default.
> > >
> >
> > And this is the problem, there is no reason anyone should have to edit
> > the kernel command line for choosing a power policy setting. Gnome is
> > certainly not the only desktop in use, practically all of the
> > documentation out there explains how to enable or disable hibernate
> > with common tools. We are invalidating all of that documentation just
> > so that gnome can implement a bad default policy. Agreeing that we
> > should not use it by default doesn't mean we should make it any harder
> > to use than it already is. We certainly have no motivation to
> > discourage people for giving it a try, they just have to know that
> > they are hibernating, and have chosen to do so. I would be just fine
> > with it being easier to access in gnome than installing gnome-tweaks,
> > hibernate, if supported by the system, could be easily selected under
> > the power menu in settings.
> >
> > > I expect the kernel changes for this to be about 3 lines of
> > > actual code (+a 15 lines or so Kconfig addition) and I expect
> > > this to go upstream without much issues as this seems like
> > > an entirely reasonable thing to do.
> > >
> > > Reading further along the discussion you say that if this
> > > were a new feature you would likely agree to defaulting it
> > > to off. But since this has been there for years we should
> > > not change it ? That seems like a weak argument to me, we
> > > have always been doing this in a sub-optimal way so lets
> > > continue doing this in a sub-optimal way ?
> > >
> > I don't agree that the way we have been doing this is sub-optimal at
> > all. In fact, I think this proposed patch is the sub-optimal way. My
> > point is, new features, particularly with possible undesirable
> > results, are often defaulted to off under a "tech preview" model. The
> > mechanism in the kernel is not new. it may not work for everyone, but
> > it has been working fairly well for those who it does work for. Why
> > would we change them when a piece of userspace (that some of them
> > might never even use) wants to create a poor default policy?
> >
> > > I agree that we should not change it in the middle of a
> > > Fedora cycle. Hence I wrote:
> > >
> > > > > Against:
> > > > >
> > > > > Currently we do have some users using hibernation without
> > > > > adding any options to the kernel commandline. These users
> > > > > will have to now add "hibernate=yes" to their kernel commandline.
> > > > >
> > > > > I'm thinking that yes we want this, but maybe this needs to
> > > > > go through the change process for proper communication, so for
> > > > > F29 we need another fix, and we can do this for F30?
> > >
> > > I believe that if we put this through the change process,
> > > we can make sure that we properly communicate the need to add
> > > "hinernate=yes" to the kernel commandline for people who use
> > > it and want to keep using it.
> > >
> > > I also expect this to, if anything, lower the load for the Fedora
> > > kernel team, since it avoids users enabling hibernation without
> > > really knowing what they are doing and then filing bugs as a result
> > > of this. E.g.:
> > > * ATM in F28 hibernation is a simple click in gnome-tweaks away.
> > > * Even if we revert the GNOME change which triggered this discussion
> > > many other DEs will still advertise hibernate support in some way.
> > >
> > > Can you please elaborate a bit on your objections against this?
> > >
> >
> > It really is simple. You don't cripple a mechanism so that you can
> > install a bad default policy. The kernel is providing a plain and
> > neutral mechanism here. If people agree that the default policy is
> > wrong, it is the policy that should change. While I strongly feel
> > that the default power behavior should not be hibernate, I also fee
> > pretty strongly that it should be very easy to people to change.
>
> Ok fair enough. Keeping it easy for users to try out hibernate is
> a valid argument.
>
> So that puts the ball back into the court of the GNOME devs, adding
> Benjamin (g-s-d co-maintainer) to the Cc and I'll also ping him
> on IRC about this.
So, it still looks like we are at a bit of a dead end with this
discussion. We know we need to disable the use of hibernation by
default but where depends on how you look at the issue (is it a policy
issue or are features falsely advertised).
>From a GNOME Settings Daemon perspective I am tempted to simply remove
the feature again. There are two main reasons for considering this:
1. It would solve the pressing issue for F29.
2. The current implementation is incomplete and causes
inconsistencies for users.
I only realised the issue with 2. when looking into it more because of
this discussion. We currently have at least 6 reasons to suspend with
different components creating the policy:
* lid action:
- systemd-logind
- gsd-power inhibits in some cases
* power button:
- gsd-media-keys: power-button-action
gsd-power settings keys
* soft button:
- gnome-shell: hardcoded to suspend (logind call)
* user is idle
- gsd-power: sleep-inactive-ac-type, sleep-inactive-battery-type
gsd-power settings keys
* battery critical:
- upower: /etc/UPower/UPower.conf (defaults to hybrid suspend)
* screen blanking:
- gsd-power: hardcoded to suspend on tablets
The patches that introduced the policy only made the change for the
"power button" and "user is idle" cases (and "screen blanking"). In
particular the "soft button" and "lid" cases are not covered, meaning
that in many cases users will not actually suspend-then-hibernate[1].
So, my proposal from the g-s-d side is:
1. For the *stable* release cycle, hide the new "feature" behind a
compile time switch, disable it by default and announce properly
in the release notes.
2. For the unstable release cycle plan on finding a more consistent
solution to control the policy.
Whether this is user configurable or not could still be something
to discuss.
I would be happy if the underlying CanSuspendThenHibernate and
CanSuspend calls would not be advertising features that are unusable.
My personal view is that it would be good if these calls were only
advertising the feature if it actually works, but I also see how this
can be hard or impossible to detect.
If systemd (or the kernel) is adjusted, then g-s-d may not need a
change. But even then it may still make sense to allow disabling the
new behaviour just to avoid the policy inconsistencies in the short
term.
Regards,
Benjamin
[1] Which probably explains why I have not personally run into this
issue yet as I personally use the two unaffected methods.
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