Messages in this thread | | | Date | Wed, 5 Dec 2001 16:26:21 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: Scheduler Cleanup |
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On Wed, 5 Dec 2001, Mike Kravetz wrote:
> On Wed, Dec 05, 2001 at 03:44:42PM -0800, Davide Libenzi wrote: > > Anyway me too have verified an increased latency with sched_yield() test > > and next days I'm going to try the real one with the cycle counter > > sampler. > > I've a suspect, but i've to see the disassembly of schedule() before > > talking :) > > One thing to note is that possible acquisition of the runqueue > lock was reintroduced in sys_sched_yield(). From looking at > the code, it seems the purpose was to ?add fairness? in the case > of multiple yielders. Is that correct Ingo?
Yep, suppose you've three running tasks A, B and C ( in that order ) and suppose A and B are yield()ing. You get:
A B A B A B A B A B A ...
until the priority of A or B drops, then C has a chance to execute. Since with the new counter decay code priority remains up until a sudden drop, why don't we decrease counter by K ( 1? ) for each sched_yield() call ? In this way we can easily avoid the above pattern in case of multiple yield()ers.
PS: sched_yield() code is very important because it is used inside the pthread spinlock() wait path for a bunch of times before falling into usleep().
- Davide
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