DragonFly kernel List (threaded) for 2007-09
Re: Detangle lwkt_switch() and the idle thread and consolidate sleep variables
Matthew Dillon wrote:
I wouldn't worry too much about tokens or the MP lock. It probably isn't
worth the effort to make those MWAITable because the scheduler
interactions are fairly complex. If the scheduler can't get the tokens
or MP lock required for a thread it continues to look for other runnable
threads. If it can't find any it loops to the top and tries again. If
multiple runnable threads were skipped due to not being able to get tokens
or the MP lock there is no easy way to use MWAIT.
That's exactly my concern. I guess we don't use so many tokens anymore,
but as long as we use the MP lock, we'll have this issue. And it would
be nice if we could use WMAIT in this case.
Then we can use MONITOR and MWAIT in both the spinlock contended
procedure and in the idle loop without having to physically disable
Yes, we should even use this directly, without doing this backoff dance.
There is no sense in running NOPs if we could instead simply wait
until the lock gets updated.
However the code right now doesn't look like it was written with this in