Date: Thu, 11 Nov 2004 17:55:52 -0500 From: Stephan Uphoff <ups@tree.com> To: Anurekh Saxena <anurekh@gmail.com> Cc: freebsd-i386@freebsd.org Subject: Re: kernel: return from interrupt Message-ID: <1100213752.78635.32.camel@palm.tree.com> In-Reply-To: <aa26c8a904111109581723563d@mail.gmail.com> References: <aa26c8a904111109581723563d@mail.gmail.com>
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On Thu, 2004-11-11 at 12:58, Anurekh Saxena wrote:
> Hi,
>
> I was under the impression that the 5.3 release had an option for full
> preemption.
> If I am correct, why does the kernel refuse to schedule on a
> return_from_interrupt if its not
> going back to userland?
> I can understand this being a problem if interrupts were nested, or
> return from a page fault in a
> critical section.
> Please correct me if I am wrong, but if a *high* priority interrupt
> thread is ready to run, it
> should be given a chance. Presuming the *interrupted* kernel path is
> going to give up the CPU
> fast enough is probably not a good idea.
>
>
> I hope I have sent this to the right mailing list.
>
> Thanks,
> Anurekh
This should work if you have "options PREEMPTION" in your config file.
You may also want to try "options FULL_PREEMPTION".
Can you describe your problems / observations?
The exception seems to be fast interrupts.
You may want to try the following untested patch to allow preemption
triggered by fast interrupts.
Index: intr_machdep.c
===================================================================
RCS file: /cvsroot/src/sys/i386/i386/intr_machdep.c,v
retrieving revision 1.11
diff -u -r1.11 intr_machdep.c
--- intr_machdep.c 3 Nov 2004 18:03:06 -0000 1.11
+++ intr_machdep.c 11 Nov 2004 22:31:19 -0000
@@ -205,7 +205,9 @@
isrc->is_pic->pic_eoi_source(isrc);
error = 0;
/* XXX */
+#if 0
td->td_pflags &= ~TDP_OWEPREEMPT;
+#endif
critical_exit();
} else {
/*
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