* [Qemu-devel] TCG slowdown
@ 2011-08-20 20:51 Edgar E. Iglesias
2011-08-20 22:37 ` Jan Kiszka
0 siblings, 1 reply; 3+ messages in thread
From: Edgar E. Iglesias @ 2011-08-20 20:51 UTC (permalink / raw)
To: qemu-devel; +Cc: jan.kiszka
Lately, my TCG emulated machines have been running terribly slow.
Like a factor 3 or 4 slower, hardly usable.
I bisected it to this:
commit d5ab9713d2d4037fd56b0adddd26c8d4dc11cf09
Author: Jan Kiszka <jan.kiszka@siemens.com>
Date: Tue Aug 2 16:10:21 2011 +0200
Avoid allocating TCG resources in non-TCG mode
Do not allocate TCG-only resources like the translation buffer when
running over KVM or XEN. Saves a "few" bytes in the qemu address space
and is also conceptually cleaner.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
It turns out that the init of the tb cache is now moved to before ram_size
gets it's default value. And because the default tb cache size, if no
-tb-size option is given, is based on the ram_size it is now zero..
Cheers
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [Qemu-devel] TCG slowdown
2011-08-20 20:51 [Qemu-devel] TCG slowdown Edgar E. Iglesias
@ 2011-08-20 22:37 ` Jan Kiszka
2011-08-20 23:05 ` Edgar E. Iglesias
0 siblings, 1 reply; 3+ messages in thread
From: Jan Kiszka @ 2011-08-20 22:37 UTC (permalink / raw)
To: Edgar E. Iglesias; +Cc: qemu-devel
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On 2011-08-20 13:51, Edgar E. Iglesias wrote:
> Lately, my TCG emulated machines have been running terribly slow.
> Like a factor 3 or 4 slower, hardly usable.
>
> I bisected it to this:
>
> commit d5ab9713d2d4037fd56b0adddd26c8d4dc11cf09
> Author: Jan Kiszka <jan.kiszka@siemens.com>
> Date: Tue Aug 2 16:10:21 2011 +0200
>
> Avoid allocating TCG resources in non-TCG mode
>
> Do not allocate TCG-only resources like the translation buffer when
> running over KVM or XEN. Saves a "few" bytes in the qemu address space
> and is also conceptually cleaner.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>
>
> It turns out that the init of the tb cache is now moved to before ram_size
> gets it's default value. And because the default tb cache size, if no
> -tb-size option is given, is based on the ram_size it is now zero..
Yes, already stumbled over that regression myself. See
http://thread.gmane.org/gmane.comp.emulators.qemu/113547
Jan
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] TCG slowdown
2011-08-20 22:37 ` Jan Kiszka
@ 2011-08-20 23:05 ` Edgar E. Iglesias
0 siblings, 0 replies; 3+ messages in thread
From: Edgar E. Iglesias @ 2011-08-20 23:05 UTC (permalink / raw)
To: Jan Kiszka; +Cc: qemu-devel
On Sat, Aug 20, 2011 at 03:37:09PM -0700, Jan Kiszka wrote:
> On 2011-08-20 13:51, Edgar E. Iglesias wrote:
> > Lately, my TCG emulated machines have been running terribly slow.
> > Like a factor 3 or 4 slower, hardly usable.
> >
> > I bisected it to this:
> >
> > commit d5ab9713d2d4037fd56b0adddd26c8d4dc11cf09
> > Author: Jan Kiszka <jan.kiszka@siemens.com>
> > Date: Tue Aug 2 16:10:21 2011 +0200
> >
> > Avoid allocating TCG resources in non-TCG mode
> >
> > Do not allocate TCG-only resources like the translation buffer when
> > running over KVM or XEN. Saves a "few" bytes in the qemu address space
> > and is also conceptually cleaner.
> >
> > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> > Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> >
> >
> > It turns out that the init of the tb cache is now moved to before ram_size
> > gets it's default value. And because the default tb cache size, if no
> > -tb-size option is given, is based on the ram_size it is now zero..
>
> Yes, already stumbled over that regression myself. See
> http://thread.gmane.org/gmane.comp.emulators.qemu/113547
OK, thanks. I've pushed your fix.
Cheers
^ permalink raw reply [flat|nested] 3+ messages in thread
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2011-08-20 20:51 [Qemu-devel] TCG slowdown Edgar E. Iglesias
2011-08-20 22:37 ` Jan Kiszka
2011-08-20 23:05 ` Edgar E. Iglesias
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