[haiku-development] Re: Disabling CPU disabling
- From: Alexander von Gluck IV <kallisti5@xxxxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Thu, 24 Oct 2013 19:01:06 -0500
On Thu, 24 Oct 2013 19:23:55 -0400
John Scipione <jscipione@xxxxxxxxx> wrote:
> On Thu, Oct 24, 2013 at 7:11 PM, Pawel Dziepak <pdziepak@xxxxxxxxxxx> wrote:
> > Since the scheduler code has grown quite big I am trying to remove as
> > much unnecessary logic as possible. The thing that caught my attention
> > is the possibility to disable a logical processor.
> >
> > As far as I understand there are two undocumented (i.e. BeBook doesn't
> > mention them but some old apps, e.g. Pulse, use them) syscalls
> > set_cpu_enabled and cpu_enabled that allow disabling/enabling a CPU
> > and check whether CPU is enabled. I don't really see why anyone would
> > like to use that. Definitely not for performance reasons. If because
> > of the energy consumption then the new scheduler has power saving mode
> > with small task packing which tries to keep as little CPUs running as
> > possible.
> >
> > So, unless there is any situation it may be useful to manually disable
> > CPU that I am missing, I am going to remove that feature (the menu in
> > Deskbar for disabling CPUs could be replaced by menu for choosing the
> > scheduler operating mode once public API for that is done).
> > _kern_set_cpu_enable and _kern_cpu_enable have to stay tough (unless
> > my assumption that they are part of the original BeOS ABI is wrong)
> > but can be implemented totally in libroot returning respectively B_OK
> > and true without even calling the kernel.
> >
> > Anyone going to miss that feature?
>
> It's a neat feature allowing you to test the system under load by
> dynamically turning a pocessors on and off to see the difference. I
> would definitely miss the feature if it were removed.
+1. I would definitely miss it. While it's usefulness is limited, it is
almost always the first thing I demo to techie people (and can wow them with)
So... -1 on removing it.
-- Alex
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