Re: [patch] CFS scheduler, -v5

Ingo Molnar
2007-04-23T03:09:07Z

* Gene Heskett <gene.heskett@gmail.com> wrote:

> I haven't approached that yet, but I just noticed, having been booted
> to this for all of 5 minutes, that although I told it not to renice x
> when my script ran 'make oldconfig', and I answered n, but there it
> is, sitting at -19 according to htop.
>
> The .config says otherwise:
> [root@coyote linux-2.6.21-rc7-CFS-v5]# grep RENICE .config
> # CONFIG_RENICE_X is not set
>
> So v5 reniced X in spite of the 'no' setting.

Hmm, apparently your X uses ioperm() while mine uses iopl(), and i only
turned off the renicing for iopl. (I fixed this in my tree and it will
show up in -v6.)

> Although I hadn't noticed it, one way or the other, I just set it (X)
> back to the default -1 so that I'm comparing the same apples when I do
> compare.

note that CFS handles negative nice levels differently from other
schedulers, so the disadvantages of agressively reniced X (lost
throughput due to overscheduling, worse interactivity) do _not_ apply to
CFS.

I think the 'fair' setting would be whatever the scheduler writer
recommends: for SD, X probably performs better at around nice 0 (i'll
let Con correct me if his experience is different). On CFS, nice -10 is
perfectly fine too, and you'll have a zippier desktop under higher
loads. (on servers this might be unnecessary/disadvantegous so there
this can be turned off.)

(also, in my tree i've changed the default from -19 to -10 to make it
less scary to people and to leave more levels to the sysadmin, this
change too will show up in -v6.)

Ingo