Warp wrote:
>   In my experience even if there is only one single CPU-intensive process
> running at nice level 19 it will run slower than if it was running eg. at
> nice level 4 (which is the default for nice when you don't specify a
> number).

The "task scheduler" (BOINC) already sets tasks at nice 19, using system
calls. I'm not manually running it with the 'nice' command.

If there is nothing else to use CPU, why would nice 19 be slower than nice
4?

>   I'm not exactly sure why this is so nor do I have any references to
>   this,
> but it's what I have experienced. Maybe a process at nice level 19 really
> is at the very bottom of the barrel and *anything* will override it, no
> matter how light. For this reason whenever I want to make a process (such
> as povray) run with a lower scheduling priority I just use the default
> nice level (ie. 4). That seems to give basically all free CPU to the
> process but will not hinder other processes which temporarily need it
> more. Also in this case the nice 4 process still gets a fair share of the
> CPU and doesn't get completely halted.
> 
>   Also in my experience nice level 4 is completely enough to keep a heavy
> process, well, nice. For example I have run long povray renders with nice
> level 4 and at the same time watched videos with mplayer without any
> problems.
> 
>   I suppose the only cases where you want to use a nice value different
> from 4 is when you want two or more heavy processes running at the same
> time and you want one of them getting more CPU than the others. The
> difference in priorites will affect how the CPU is shared between them.

Interestingly there have been some BOINC users complaining that even at nice
19, if a user process tries to use all the CPU at nice 0, the BOINC app
will still use 5% of CPU.

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Nicolas Alvarez wrote
> The "task scheduler" (BOINC) already sets tasks at nice 19, using system
> calls. I'm not manually running it with the 'nice' command.

Since I'm already running a version I compiled from source (and modified
quite a bit), I could change the nice level if I wanted to...


There is also new problems now that there are GPGPU applications. When
running at low priority, the application computed REALLY slow. The GPU
starved because the CPU couldn't feed it with data often enough.

But if the app ran at normal priority, it used like 2% of CPU, so it didn't
make the machine slow... So now GPU apps are run at normal priority. (there
is still a problem on Windows, where it's using over 20% CPU).

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Warp wrote:
>   Also in my experience nice level 4 is completely enough to keep a heavy
> process, well, nice. 

I think that's probably true of CPU-bound processes. I've had trouble 
getting I/O bound processes to play well with others (under both XP and 
Linux) because the nice value doesn't affect them. Plus, the "ionice" 
bit seems pretty primitve, and the ionice processes don't run unless you 
completely stop using the disk for several seconds, it seems.

Unfortunately, most of my actual paying work is I/O bound, not CPU bound.

-- 
Darren New / San Diego, CA, USA (PST)

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