* Jarek Poplawski <jarkao2@xxxxx> 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 <mingo@xxxxxxx> 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. */ - To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
