cvs commit: src/sys/cam/scsi scsi_target.c src/sys/coda coda_psdev.c src/sys/dev/aac aac.c src/sys/dev/bktr bktr_core.c src/sys/dev/firewire firewire.c src/sys/dev/kbd kbd.c src/sys/dev/nmdm nmdm.

[Seigo Tanimura]

On Tue, 11 Nov 2003 04:16:15 +1100 (EST),
  Bruce Evans <bde at zeta.org.au> said:

bde> On Mon, 10 Nov 2003, Seigo Tanimura wrote:
>> On Mon, 10 Nov 2003 18:14:14 +1100 (EST),
>> Bruce Evans <bde at zeta.org.au> said:

>> ...
bde> set the thread priority using that.  So this changes is needed to get the
bde> same behaviour as using tsleep().  However, I think that behaviour is not
bde> quite right -- if the thread is a user thread then it waking it up is only
bde> urgent if it needs to do some urgent things in kernel mode on wakeup.  It
bde> should not return to user mode until its user priority permits its
bde> scheduling.  However2, we still have the bugfeature that user threads keep
bde> the kernel priority that they wake up at all the way back to user mode,
bde> and this may be necessary for interactivity.
>> 
>> I could implement priority bumping in selwakeuppri(), but I thought it
>> would be troublesome to tweak struct cv outside kern_condvar.c.
>> 
>> In case of select(2) et. al., selecting threads waken up repolls file
>> descriptors.  As it is a in-kernel work, those threads should remain
>> at in-kernel priorities until polling succeeds, aren't they?

bde> I think there is no need for elevated kernel priority in select() if
bde> threads drop back to their normal user priority on return to user mode,
bde> since nothing (?) except the user process is affected by the results
bde> of select() (unlike for some i/o operations).  Note that the priority

That would hold if a thread waken up went straightly back to user
mode.


bde> is not elevated at the start of select(), so processes can be preempted
bde> there now that we have a semi-preempive kernel.  Why should the
bde> completion of select() be different if the thread needed to sleep?
bde> Any increase in priority should be because the thread slept for a while
bde> and not arbitrary.

We may need some tricks to protect all of the file descriptors being
polled in kern_select().

-- 
Seigo Tanimura <tanimura at tanimura.dyndns.org> <tanimura at FreeBSD.org>