[Xen-devel] Possible bugs and doubts about readjusting weights/slice-lengths from command prompt

["Amitayu Das" <amitayudas@xxxxxxxxx>]

Hi,

I had few doubts/questions about readjusting slice/period length (or
weights) for domains from command prompt. If someone can clarify,
that'd be very nice. Here is the list (with respect to sedf scheduler):

1. Is is true that mentioning weights for a domain is setting a maximum
limit for it so that it can't go beyond that limit by setting extra
flag on? If that's the case, why in xen/common/scehd_sedf.c, a checking
for extra flag is being made at first:

    if ( cmd->direction == SCHED_INFO_PUT )
    {
     ...
        if (cmd->u.sedf.weight) {
            if ((cmd->u.sedf.extratime & EXTRA_AWARE) &&
                (! cmd->u.sedf.period)) {
               
/*weight driven domains with xtime ONLY!*/
      ...

Please let me know if I'm missing something.

2. Say, I'm readjusting the slice lengths of running domains. While
doing that, I make a mistake by having sum of the slice-lengths higher
than period-length. In such cases, what does Xen actually do? I did not
find sanity-checking code for such cases in xen/common/sched_sedf.c.
Please let me know in case it's not there, why so or it's there, only I
did not find it.

3. I tried to modify/readjust the slice/period length (or weights) for
domains from command prompt.  However, I  found out
that  changes are immaterial after first attempt. That is, no
matter what changes I made at second or third or fourth time, they are
not actually taking place. Only, the changes made during the first
attempt actually took place. Please let me know if this is a bug in the
existing code or I should have done the things in a different manner.

Thanks in advance,
Amitayu
     

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