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.
