wakeup_flags patch.

[Jeff Roberson]

On Mon, 2 Jul 2007, John Baldwin wrote:

> On Sunday 01 July 2007 07:08:35 pm Jeff Roberson wrote:
>> http://people.freebsd.org/~jeff/wakeupflags.diff
>>
>> It didn't workout very cleanly since the flags have to go through three
>> layers.  I could define wakeup and sleepq flags to be the same and skip a
>> bunch of conditionals.  However, we'd then have to know which flags were
>> free to use in each case.  Are there any further opinions on the style?
>>
>> This patch does not include an implementation for WAKEUP_LOCAL.  I'm still
>> working on that in SCHED_SMP.  Ironically, it does include an
>> implementation for WAKEUP_TAIL, however, I don't have any users of that.
>> :-)
>
> You can find the pre-threadlock patch for 7.x of what Y! uses for accept() at
> www.freebsd.org/~jhb/patches/justone.patch
>
> It has two features your WAKEUP_TAIL doesn't have (one of which I mentioned
> earlier): 1) it doesn't wakeup threads from swapped out processes (you aren't
> getting a thread that is "hot" in the cache if you have to go page it back in
> from disk), and 2) it returns a success/fail to the caller so that it can
> fallback to its traditional behavior if we couldn't find a "hot" thread to
> resume.

Shouldn't we simply choose a non-hot thread in this case?  In your 
environment is it common to have a lot of swapped out proceses?  It would 
be expensive to lock and unlock each thread to check if it's swapped. 
Perhaps we can simply do it in a racey way.

Jeff

>
> -- 
> John Baldwin
>