On Thu, Feb 02, 2012 at 03:24:46PM -0800, Eric W. Biederman wrote: > > Eric, brought up a point that because the boot code was restructured we may > > not need to disable the io apic any more in the crash path. The original > > concern that led to the development of disable_IO_APIC, was that the TSC > > calibration on boot up relied on the PIT timer for reference. Access > > to the PIT required 8259 interrupts to be working. This wouldn't work > > if the ioapic needed to be configured. So on panic path, the ioapic was > > reconfigured to use virtual wire mode to allow the 8259 to passthrough. > > A small clarification originally it was the jiffies calibration that > would fail if we could cause the PIT to generate interrupts through the > 8259. The boot would then hang at calibrating jiffies. Ok. Thanks! > > > Those concerns don't hold true now, thanks to the fast TSC calibration code > > not needing the PIT. As a result, we can remove this call and simplify the > > locking needed in the panic path. > > > > I tested kdump on an Ivy Bridge platform, a Pentium4 and an old athlon that > > did not have an ioapic. All three were successful. > > > > Cc: Eric W. Biederman <ebiederm at xmission.com> > > Cc: Vivek Goyal <vgoyal at redhat.com> > > Signed-off-by: Don Zickus <dzickus at redhat.com> > > > > --- > > I will probably need some help with my explaination as to why this line is not > > needed. Any input is appreciated! > > Can you test and verify that we also do not need the lapic_shutdown() > call and the disable_local_APIC call on the other processors. The same > reasoning that supports us not needing to disable the IO_APIC also > supports us not needing to disable local apic. I did that and it seemed to work on my Ivy Bridge and core2 quad systems. > > Removing disable_IO_APIC in and of itself and then booting isn't quite > sufficient as a practical test to prove this code always works. > Sometimes the IOAPIC was not hooked up to interesting interrupt sources > like the 8259. So what systems should I look for to test? Cheers, Don
