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SubjectRe: [RFC][PATCH] O(1) Entitlement Based Scheduler
Peter Williams wrote:
> Timothy Miller wrote:
>
>> How about this:
>>
>> The kernel tracks CPU usage, time slice expiration, and numerous other
>> statistics, and exports them to userspace through /proc or somesuch.
>> Then a user-space daemon adjusts priority.
>
>
> Yes, the right statistics could allow these processes to be identified
> reasonably accurately. The programs in question would have the
> following characteristics:
>
> 1. low CPU usage rate, and
> 2. a very regular pattern of use i.e. the size of each CPU bursts would
> be approximately constant as would the size of the intervals between
> each burst.

There is no need for the regularity. When I use a word processor, I
use it very irregularly. Sometimes I type text, and wants each letter
typed to appear instantly. This fits well with "low cpu usage" and
sudden short bursts. There may be lots of long delays though while
I think about stuff to write. So the intervals are irregular, I still
believe I should get the boosts as long as the bursts are small.
Doing something big (such as invoking latex on a big document)
is cpu-heavy, but then it is ok not to get the boost.
Current schedulers based on io-waiting gets this right already.
>
> The appropriate statistic to identify the second of these would be
> variance or (equivalently but more expensively) standard deviation.
> Whether this problem is bad/important enough to warrant the extra
> overhead of gathering these statistics is a moot point. We had to
> generate very high system loads on a single CPU system in order to cause
> one or two skips in xmms over a period of a couple of minutes.

Well, perhaps you could give a slightly bigge boost to a very regular
thing like xmms. But even that might have some snags, the load
might change a lot when doing midi in software, depending on how
many instruments are active simultaneously. There goes the
constant-size bursts.

Helge Hafting

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