* Jarek Poplawski <[email protected]> wrote:
> > > > + }
> > > > #ifdef CONFIG_HARDIRQS_SW_RESEND
> >
> > we used the hw-resend method unconditionally, right?
>
> Right: unconditionally on a condition they are not edges...
>
> But, since not resending at all seems to work so good in testing, I
> thought, _SW_RESEND could be considered as an unnecessarily
> complicated alternative.
>
> Now, I'm a bit confused...
the idea is multi-pronged:
- Primarily, we want to fix the regression. 2.6.20 worked, 2.6.21
didnt, that has to be fixed, no matter what - end of story. But we've
got a wide selection of patches for that purpose now, so what matters
at this point is the secondary question:
- we want to know _why exactly_ the hang happens. We now have a pretty
good theory: hw-resend hangs the IO-APIC. (there is a delicate dance
between local APICs and IO-APICs for level-triggered irqs, and if we
interject via hw-resending via the local APIC, existing races, hw
bugs or weaknesses in our hw-resend implementation might be exposed)
and even though we now have a wide selection of patches we really want
to get to the bottom of the problem so that we can fix the bug that got
exposed: apparently hw resend doesnt always work with level-triggered
irqs.
Note that the hw-resend sequence can trigger _even without our original
patch that triggered the regression_, it's just much less likely to
happen, so this is a pre-existing IO-APIC/APIC code bug that could
trigger anytime, and which we want to see fixed.
To confirm this theory - does the debug-patch below fix the hang? If it
fixes the hang then the theory is confirmed and then the right solution
is to retrigger an IRQ for level-triggered irqs with the proper
trigger-type set.
Ingo
------------------>
Not-Signed-off-by: Ingo Molnar <[email protected]>
Index: linux/arch/i386/kernel/io_apic.c
===================================================================
--- linux.orig/arch/i386/kernel/io_apic.c
+++ linux/arch/i386/kernel/io_apic.c
@@ -735,7 +735,8 @@ void fastcall send_IPI_self(int vector)
* Wait for idle.
*/
apic_wait_icr_idle();
- cfg = APIC_DM_FIXED | APIC_DEST_SELF | vector | APIC_DEST_LOGICAL;
+ cfg = APIC_DM_FIXED | APIC_DEST_SELF | vector | APIC_DEST_LOGICAL |
+ APIC_INT_LEVELTRIG;
/*
* Send the IPI. The write to APIC_ICR fires this off.
*/
-
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