On 10/14/2011 12:36, andrel wrote:
>> You really don't want the guy at the keyboard hitting CAD and suspending
>> your corporate web server.
>
> Nor do you want him to effectively freeze it for 10 minutes by doing
> something stupid. See also below.

Agreed.

>>> Because the task manager is implemented at the same priority level as
>>> Blender?
>>
>> No it isn't. The problem isn't with the CPU. The problem is with the
>> disk.
>
> IIRC you have said that before. Actually several times and I have never
> contradicted you.

Well, sure. But the problem is that nobody implements effective disk 
priorities any more (which is what I'm saying), so just saying "priority" 
implies CPU priority.

> Actually my point is that it *should not* be a user program.

That's likely true.  However, the frequency with which this happens probably 
doesn't warrant a kernel mechanism for a UI for picking a task and killing 
it, either. Especially since many times it happens, it's nothing to do with 
a task that's still running that you could actually do anything about.

Indeed, it would seem what you'd really want is a way to indicate that if a 
job got to the point where it was paging too often, that would be enough to 
kill it or deprioritize its disk I/O, to the point of suspending it for a 
second or more each time some other process went after the disk, sort of 
like how Linux (seems to) does "low priority" disk I/O.

> I know that (long, long time ago I studied OS's a bit). I obviously meant
> the part of the kernel (and user level program in badly designed systems)
> that handles the CAD.

Oh, well, you want an entire process management system built into the 
kernel, invocable by a simple keystroke. Probably not realistic in modern OSes.

> I disagree, there is no other user on my machine than me*. And that is also
> why your corporate webserver is a wrong example. webservers and user
> machines are something different. You should not mix those.

If your corporate web server is thrashing, how are you going to stop it?

> OS should behave different. Specifically in the area that we are discussing.
> CAD on a webserver should leave everything running (probably should even be
> disabled), but when I press CAD on my keyboard because I want control, i
> *want control* and I know what other processes I am also stopping.

Well, as the Linux enthusiasts would say, "we eagerly await your patch." :-)

CAD should certainly not be disabled on a web server, as it does far more 
than just bring up the task manager. That's the other half of the problem.

In pretty much every situation other than disk thrashing, CAD works pretty 
much instantly. In many cases of disk thrashing, there's nothing you can do 
about it, like my example of sync'ing gigabytes of changes to the disk. And 
modern OSes are set up to treat file reading and page faulting as 
essentially similar in many ways (and then there's memmap, which adds 
another confusion on top), so it's not really even obvious when there's 
thrashing which process is causing it or what to do about it, because it's 
entirely possible there wouldn't be thrashing if there weren't 3 or 4 
programs all doing something at once.

> *) that is at least my view of the machine. Technically it is not true.

Well, that's kind of the point I'm making. :)

-- 
Darren New, San Diego CA, USA (PST)
   How come I never get only one kudo?

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