Re: [PATCH] scheduler fixups ...

[Davide Libenzi]

On 3 Jan 2002, Peter Osterlund wrote:

> Davide Libenzi <[e-mail]> writes:
>
> > On 2 Jan 2002, Peter Osterlund wrote:
> >
> > > Davide Libenzi <[e-mail]> writes:
> > >
> > > > a still lower ts
> > >
> > > This also lowers the effectiveness of nice values. In 2.5.2-pre6, if I
> > > run two cpu hogs at nice values 0 and 19 respectively, the niced task
> > > will get approximately 20% cpu time (on x86 with HZ=100) and this
> > > patch will give even more cpu time to the niced task. Isn't 20% too
> > > much?
> >
> > The problem is that with HZ == 100 you don't have enough granularity to
> > correctly scale down nice time slices. Shorter time slices helps the
> > interactive feel that's why i'm pushing for this.
>
> OK, but even architectures with bigger HZ values will suffer. Isn't it
> better to set MIN_NICE_TSLICE to a smaller value (such as 1000) and
> fix the calculation in fill_tslice_map to make sure ts_table[i] is
> always non-zero. The current formula will break anyway if
>
>         HZ < 1000000 / MIN_NICE_TSLICE = 100,
>
> but maybe HZ >= 100 is true for all architectures?

Yep, but we can do something like :

static void fill_tslice_map(void)
{
    int i;

    for (i = 0; i < NICE_RANGE; i++) {
        ts_table[i] = ((MIN_NICE_TSLICE +
                        ((MAX_NICE_TSLICE - MIN_NICE_TSLICE) /
                         (NICE_RANGE - 1)) * i) * HZ) / 1000000;
        if (!ts_table[i]) ts_table[i] = 1;
    }
}

- Davide