[Qemu-devel] default guest RAM size?

[Qemu-devel] default guest RAM size?

[Michael Tokarev]

For many years, qemu defaults to 128Mb of guest RAM size.
Today, this is just too small, and many OSes fails to boot
with this size, more, they fail to produce any reasonable
messages either (eg, windows7 just crashes at startup).

Some distributions (eg ubuntu) had a local patch to increase
this value, for years.

Maybe it's time to increase the default RAM size a bit?
Make it arch-specific if needs to be ?

Thanks,

/mjt

Re: [Qemu-devel] default guest RAM size?

[Peter Maydell]

On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
> For many years, qemu defaults to 128Mb of guest RAM size.
> Today, this is just too small, and many OSes fails to boot
> with this size, more, they fail to produce any reasonable
> messages either (eg, windows7 just crashes at startup).

If you make the default bigger then some boards will crash
or behave weirdly because they try to map more RAM in than
will fit into the space for RAM in their address maps.

> Some distributions (eg ubuntu) had a local patch to increase
> this value, for years.
>
> Maybe it's time to increase the default RAM size a bit?
> Make it arch-specific if needs to be ?

I tried two years ago to get a 'default RAM size' parameter
added to the QEMUMachine struct, but the patchseries got shot
down because it didn't attempt to address NUMA / simulate
the fact you can only add RAM one DIMM at a time / etc...

http://lists.gnu.org/archive/html/qemu-devel/2011-03/msg02907.html

-- PMM

Re: [Qemu-devel] default guest RAM size?

[陳韋任 (Wei-Ren Chen)]

On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
> > For many years, qemu defaults to 128Mb of guest RAM size.
> > Today, this is just too small, and many OSes fails to boot
> > with this size, more, they fail to produce any reasonable
> > messages either (eg, windows7 just crashes at startup).
> 
> If you make the default bigger then some boards will crash
> or behave weirdly because they try to map more RAM in than
> will fit into the space for RAM in their address maps.

  So, 128Mb is still a good default? I am just wondering if those
boards with little memory still are major user of QEMU? :)

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

Re: [Qemu-devel] default guest RAM size?

[Peter Maydell]

On 5 March 2013 14:07, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw> wrote:
> On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
>> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> > For many years, qemu defaults to 128Mb of guest RAM size.
>> > Today, this is just too small, and many OSes fails to boot
>> > with this size, more, they fail to produce any reasonable
>> > messages either (eg, windows7 just crashes at startup).
>>
>> If you make the default bigger then some boards will crash
>> or behave weirdly because they try to map more RAM in than
>> will fit into the space for RAM in their address maps.
>
>   So, 128Mb is still a good default? I am just wondering if those
> boards with little memory still are major user of QEMU? :)

They may not be major but they're still in the codebase. You
can't just arbitrarily break them -- you need to propose
a path forward that doesn't do that.

-- PMM

Re: [Qemu-devel] default guest RAM size?

[Daniel P. Berrange]

On Tue, Mar 05, 2013 at 09:26:32AM +0400, Michael Tokarev wrote:
> For many years, qemu defaults to 128Mb of guest RAM size.
> Today, this is just too small, and many OSes fails to boot
> with this size, more, they fail to produce any reasonable
> messages either (eg, windows7 just crashes at startup).
> 
> Some distributions (eg ubuntu) had a local patch to increase
> this value, for years.

Out of interest, what do they change it too ?

> Maybe it's time to increase the default RAM size a bit?
> Make it arch-specific if needs to be ?

As with pretty much all QEMU hardware defaults, the default RAM
size is always going to be a tradeoff between compatibility and
optimization for specific use case. I can understand that the
current RAM setting is useless for pretty much all x86 currently
shipping "retail" operating systems (ie the ubuntu, fedora, windows,
etc of today), but that's not really the only thing to worry about
when invoking QEMU. People invoking QEMU manually have to care
about many other aspects of hardware configuration that are going
to be OS specific.

I think rather than asking the narrow question of whether we need
to increase the default RAM, we need to have a clear statement on
what target the default QEMU machine setup is aiming at.

If answer to that is that we're aiming to offer parity with current
state of the art desktop hardware specs, then clearly we should be
changing the RAM and other aspects over time to keep up. But it
could be that our aim is to just not change the default hardware
ever and explicitly state that this is a job for a layer above
QEMU to solve.

We've had similar requests periodically against libvirt to say
we should default to hardware model XYZ, or hardware config ABC.
In the end we've always pointed out that by changing the defaults
you never really solve the problem - you are just moving the
problem from one person to a different person. The concept of
virtual hardware defaults is just impossible to get right, since
this is fundamentally something that has a different answer for
every OS out there.

This is what motivated the creation of the libosinfo project. It aims
to provide a database of all the various OS specific metadata for use
by such higher level tools, and API to query this database. Included
in the metadata it maintains are the minimum, and recommended resource
settings for RAM, CPU count and disk storage for that OS, recommended
default hardware devices, location of ISO images / install trees, ISO
image signatures, release/eol dates, and much more besides.

So now when anyone askes for a change in libvirt defaults we just tell
them that the app using libvirt should be picking the OS specific
settings from libosinfo or a similar kind of source. So far only the
GNOME boxes app is using libosinfo, but I'm intending to make both
virt-manager and OpenStack use it too.

NB libosinfo has no dependency on libvirt at all - its only dep is on
GLib, so we can use GObject introspection to expose the library to
many different languages.

Regards,
Daniel
-- 
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Re: [Qemu-devel] default guest RAM size?

[Rob Landley]

On 03/05/2013 12:09:27 AM, Peter Maydell wrote:
> On 5 March 2013 14:07, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw>  
> wrote:
> > On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
> >> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
> >> > For many years, qemu defaults to 128Mb of guest RAM size.
> >> > Today, this is just too small, and many OSes fails to boot
> >> > with this size, more, they fail to produce any reasonable
> >> > messages either (eg, windows7 just crashes at startup).
> >>
> >> If you make the default bigger then some boards will crash
> >> or behave weirdly because they try to map more RAM in than
> >> will fit into the space for RAM in their address maps.
> >
> >   So, 128Mb is still a good default? I am just wondering if those
> > boards with little memory still are major user of QEMU? :)
> 
> They may not be major but they're still in the codebase. You
> can't just arbitrarily break them -- you need to propose
> a path forward that doesn't do that.

256 can be handled by most things. The powerpc, arm, and mips boards I  
use in aboriginal linux all handle 256 megs. (The main reason sh4 isn't  
a real platform is it's hardwired to 64 megs.)

(Sparc32 can handle 256 megs ram but crashes if you feed it too long a  
kernel command line.)

Rob

Re: [Qemu-devel] default guest RAM size?

[Markus Armbruster]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> For many years, qemu defaults to 128Mb of guest RAM size.
>> Today, this is just too small, and many OSes fails to boot
>> with this size, more, they fail to produce any reasonable
>> messages either (eg, windows7 just crashes at startup).
>
> If you make the default bigger then some boards will crash
> or behave weirdly because they try to map more RAM in than
> will fit into the space for RAM in their address maps.
>
>> Some distributions (eg ubuntu) had a local patch to increase
>> this value, for years.
>>
>> Maybe it's time to increase the default RAM size a bit?
>> Make it arch-specific if needs to be ?
>
> I tried two years ago to get a 'default RAM size' parameter
> added to the QEMUMachine struct, but the patchseries got shot
> down because it didn't attempt to address NUMA / simulate
> the fact you can only add RAM one DIMM at a time / etc...
>
> http://lists.gnu.org/archive/html/qemu-devel/2011-03/msg02907.html

As so often, the better we wish we had is the enemy of the good we could
have, if we weren't so pig-headed about it.

Re: [Qemu-devel] default guest RAM size?

[Peter Maydell]

On 6 March 2013 11:59, Rob Landley <rob@landley.net> wrote:
> On 03/05/2013 12:09:27 AM, Peter Maydell wrote:
>> On 5 March 2013 14:07, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw>
>> wrote:
>> > On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
>> >> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> >> > For many years, qemu defaults to 128Mb of guest RAM size.
>> >> > Today, this is just too small, and many OSes fails to boot
>> >> > with this size, more, they fail to produce any reasonable
>> >> > messages either (eg, windows7 just crashes at startup).
>> >>
>> >> If you make the default bigger then some boards will crash
>> >> or behave weirdly because they try to map more RAM in than
>> >> will fit into the space for RAM in their address maps.
>> >
>> >   So, 128Mb is still a good default? I am just wondering if those
>> > boards with little memory still are major user of QEMU? :)
>>
>> They may not be major but they're still in the codebase. You
>> can't just arbitrarily break them -- you need to propose
>> a path forward that doesn't do that.
>
> 256 can be handled by most things.

I'm going to take a wild guess that Windows 7 doesn't do any
better in 256MB than it does with 128 :-)

-- PMM

Re: [Qemu-devel] default guest RAM size?

[Michael Tokarev]

06.03.2013 22:47, Daniel P. Berrange wrote:
> On Thu, Mar 07, 2013 at 02:34:53AM +0800, Peter Maydell wrote:
>> I'm going to take a wild guess that Windows 7 doesn't do any
>> better in 256MB than it does with 128 :-)

Actually it does.  With 128Mb it crashes.  With 256Mb it says it
wants more memory.

/mjt

Re: [Qemu-devel] default guest RAM size?

[Daniel P. Berrange]

On Thu, Mar 07, 2013 at 02:34:53AM +0800, Peter Maydell wrote:
> On 6 March 2013 11:59, Rob Landley <rob@landley.net> wrote:
> > On 03/05/2013 12:09:27 AM, Peter Maydell wrote:
> >> On 5 March 2013 14:07, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw>
> >> wrote:
> >> > On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
> >> >> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
> >> >> > For many years, qemu defaults to 128Mb of guest RAM size.
> >> >> > Today, this is just too small, and many OSes fails to boot
> >> >> > with this size, more, they fail to produce any reasonable
> >> >> > messages either (eg, windows7 just crashes at startup).
> >> >>
> >> >> If you make the default bigger then some boards will crash
> >> >> or behave weirdly because they try to map more RAM in than
> >> >> will fit into the space for RAM in their address maps.
> >> >
> >> >   So, 128Mb is still a good default? I am just wondering if those
> >> > boards with little memory still are major user of QEMU? :)
> >>
> >> They may not be major but they're still in the codebase. You
> >> can't just arbitrarily break them -- you need to propose
> >> a path forward that doesn't do that.
> >
> > 256 can be handled by most things.
> 
> I'm going to take a wild guess that Windows 7 doesn't do any
> better in 256MB than it does with 128 :-)

Indeed documented min requirements for Win7 are 2 GB on x86_64. In fact
very few modern OS accept anything as low as 256 MB. If you want adefault
that is suitable for anything mainstream then we're talking GB's not MB's.

Daniel
-- 
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|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

Re: [Qemu-devel] default guest RAM size?

[Rob Landley]

On 03/06/2013 12:34:53 PM, Peter Maydell wrote:
> On 6 March 2013 11:59, Rob Landley <rob@landley.net> wrote:
> > On 03/05/2013 12:09:27 AM, Peter Maydell wrote:
> >> On 5 March 2013 14:07, 陳韋任 (Wei-Ren Chen)  
> <chenwj@iis.sinica.edu.tw>
> >> wrote:
> >> > On Tue, Mar 05, 2013 at 01:40:38PM +0800, Peter Maydell wrote:
> >> >> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
> >> >> > For many years, qemu defaults to 128Mb of guest RAM size.
> >> >> > Today, this is just too small, and many OSes fails to boot
> >> >> > with this size, more, they fail to produce any reasonable
> >> >> > messages either (eg, windows7 just crashes at startup).
> >> >>
> >> >> If you make the default bigger then some boards will crash
> >> >> or behave weirdly because they try to map more RAM in than
> >> >> will fit into the space for RAM in their address maps.
> >> >
> >> >   So, 128Mb is still a good default? I am just wondering if those
> >> > boards with little memory still are major user of QEMU? :)
> >>
> >> They may not be major but they're still in the codebase. You
> >> can't just arbitrarily break them -- you need to propose
> >> a path forward that doesn't do that.
> >
> > 256 can be handled by most things.
> 
> I'm going to take a wild guess that Windows 7 doesn't do any
> better in 256MB than it does with 128 :-)

Who cares? I meant that I got 256 megs in an arm board, 256 megs in a  
mips board, 256 megs in a powerpc board, and 256 megs in a sparc board.

KVM is welcome to change its defaults however it likes. This is the  
qemu list.

Rob

Re: [Qemu-devel] default guest RAM size?

[Peter Maydell]

On 7 March 2013 09:21, Rob Landley <rob@landley.net> wrote:
> On 03/06/2013 12:34:53 PM, Peter Maydell wrote:
>> On 6 March 2013 11:59, Rob Landley <rob@landley.net> wrote:
>> > 256 can be handled by most things.
>>
>> I'm going to take a wild guess that Windows 7 doesn't do any
>> better in 256MB than it does with 128 :-)
>
>
> Who cares? I meant that I got 256 megs in an arm board, 256 megs in a mips
> board, 256 megs in a powerpc board, and 256 megs in a sparc board.
>
> KVM is welcome to change its defaults however it likes. This is the qemu
> list.

KVM the kernel component doesn't manage default RAM size -- QEMU
does. You would have the same problems running Windows 7 on a TCG
QEMU, because there's only one place we set the default RAM size
globally for all boards. This is purely a QEMU issue which we
should fix. There's no point increasing our single default RAM
size to 256 because that fixes nothing -- it is still too small
to be a useful default for many boards.

-- PMM

Re: [Qemu-devel] default guest RAM size?

[Anthony Liguori]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 5 March 2013 13:26, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> For many years, qemu defaults to 128Mb of guest RAM size.
>> Today, this is just too small, and many OSes fails to boot
>> with this size, more, they fail to produce any reasonable
>> messages either (eg, windows7 just crashes at startup).
>
> If you make the default bigger then some boards will crash
> or behave weirdly because they try to map more RAM in than
> will fit into the space for RAM in their address maps.
>
>> Some distributions (eg ubuntu) had a local patch to increase
>> this value, for years.
>>
>> Maybe it's time to increase the default RAM size a bit?
>> Make it arch-specific if needs to be ?
>
> I tried two years ago to get a 'default RAM size' parameter

I don't see that in this series.  It's a maximum RAM size.

Anyway, there's no problem changing the default ram size (and making it
per-board).  The only requirement is that -M pc-1.4 and below continues
to expose 128MB as the default.

It's not worth bike shedding over what the default should be for pc
targets.  256 or 512 would be equally good defaults and either would be
acceptable.

Regards,

Anthony Liguori

> added to the QEMUMachine struct, but the patchseries got shot
> down because it didn't attempt to address NUMA / simulate
> the fact you can only add RAM one DIMM at a time / etc...
>
> http://lists.gnu.org/archive/html/qemu-devel/2011-03/msg02907.html
>
> -- PMM

[Qemu-devel] propose to implement ower device

[li guang]

Hi, Anthony and all

By now all devices of QEMU do not have much more
power management consideration, for example, if
system do suspend, it will call all registered notifiers,
this was loosely required, and the code to do power management
state transition seems just do 'ugly emulation', rather than be
conscious with whole system devices, same condition with reset(it
has been embedded in DeviceClass, good!),
shutdown, in real world, commonly all devices' power are controlled
by a power chip, then all power sequence can be done just
issue commands to this chip.
so, I come across an idea to implement qdev'ed power device, and
make all qdev struct of devices aware of self power management(add
reset, suspend, shutdown ... filed for DeviceClass), this will
bring tidy power management, and the emulation will more like what
happened in real world.
Hope I've expressed my idea clearly, if you have any questions, let me
know, if get your permission, I'll step ahead to do this power
chip emulation work.

Thanks!

Re: [Qemu-devel] propose to implement ower device

[Wenchao Xia]

于 2013-3-7 11:40, li guang 写道:
> Hi, Anthony and all
>
> By now all devices of QEMU do not have much more
> power management consideration, for example, if
> system do suspend, it will call all registered notifiers,
> this was loosely required, and the code to do power management
> state transition seems just do 'ugly emulation', rather than be
> conscious with whole system devices, same condition with reset(it
> has been embedded in DeviceClass, good!),
> shutdown, in real world, commonly all devices' power are controlled
> by a power chip, then all power sequence can be done just
> issue commands to this chip.
> so, I come across an idea to implement qdev'ed power device, and
> make all qdev struct of devices aware of self power management(add
> reset, suspend, shutdown ... filed for DeviceClass), this will
> bring tidy power management, and the emulation will more like what
> happened in real world.
> Hope I've expressed my idea clearly, if you have any questions, let me
> know, if get your permission, I'll step ahead to do this power
> chip emulation work.
>
> Thanks!
>
>

Hi, Guang
   it seems the mail was sent as a child mail of "Default guest RAM
size". The topic is interesting, suggest resend it.

-- 
Best Regards

Wenchao Xia

Re: [Qemu-devel] propose to implement ower device

[li guang]

在 2013-03-07四的 21:41 +0800，Wenchao Xia写道：
> 于 2013-3-7 11:40, li guang 写道:
> > Hi, Anthony and all
> >
> > By now all devices of QEMU do not have much more
> > power management consideration, for example, if
> > system do suspend, it will call all registered notifiers,
> > this was loosely required, and the code to do power management
> > state transition seems just do 'ugly emulation', rather than be
> > conscious with whole system devices, same condition with reset(it
> > has been embedded in DeviceClass, good!),
> > shutdown, in real world, commonly all devices' power are controlled
> > by a power chip, then all power sequence can be done just
> > issue commands to this chip.
> > so, I come across an idea to implement qdev'ed power device, and
> > make all qdev struct of devices aware of self power management(add
> > reset, suspend, shutdown ... filed for DeviceClass), this will
> > bring tidy power management, and the emulation will more like what
> > happened in real world.
> > Hope I've expressed my idea clearly, if you have any questions, let me
> > know, if get your permission, I'll step ahead to do this power
> > chip emulation work.
> >
> > Thanks!
> >
> >
> 
> Hi, Guang
>    it seems the mail was sent as a child mail of "Default guest RAM
> size". The topic is interesting, suggest resend it.

OK