On Thu, Dec 06, 2007 at 07:10:23PM -0500, Neil Horman wrote: > On Thu, Dec 06, 2007 at 05:11:43PM -0500, Vivek Goyal wrote: > > On Thu, Dec 06, 2007 at 04:39:51PM -0500, Neil Horman wrote: > > > On Fri, Nov 30, 2007 at 09:51:31AM -0500, Neil Horman wrote: > > > > On Fri, Nov 30, 2007 at 09:42:50AM -0500, Vivek Goyal wrote: > > > <snip> > > > > > > > > Thats what I'm doing at the moment. I'm working on a RHEL5 patch at the moment > > > > (since thats whats on the production system thats failing), and will forward > > > > port it once its working > > > > > > > > And not to split hairs, but techically thats not our _only_ choice. We could > > > > force kdump boots on cpu0 as well ;) > > > > > > > > Thanks > > > > Neil > > > > > > > > > Thanks > > > > > Vivek > > > > > > > > > > > > > Sorry to have been quiet on this issue for a few days. Interesting news to > > > report, though. So I was working on a patch to do early apic enabling on > > > x86_64, and had something working for the old 2.6.18 kernel that we were > > > origionally testing on. Unfortunately while it worked on 2.6.18 it failed > > > miserably on 2.6.24-rc3-mm2, causing check_timer to consistently report that the > > > timer interrupt wasn't getting received (even though we could successfully run > > > calibrate_delay). Vivek and I were digging into this, when I ran accross the > > > description of the hypertransport configuration register in the opteron > > > specification. It contains a bit that, suprise, configures the ht bus to either > > > unicast interrupts delivered accross the ht bus to a single cpu, or to broadcast > > > it to all cpus. Since it seemed more likely that the 8259 in the nvidia > > > southbridge was transporting legacy mode interrupts over the ht bus than > > > directly to cpu0 via an actual wire, I wrote the attached patch to add a quirk > > > for nvidia chipsets, which scanned for hypertransport controllers, and ensured > > > that that broadcast bit was set. Test results indicate that this solves the > > > problem, and kdump kernels boot just fine on the affected system. > > > > > > > Hi Neil, > > > > Should we disable this broadcasting feature once we are through? Otherwise > > in normal systems it might mean extra traffic on hypertransport. There > > is no need for every interrupt to be broadcasted in normal systems? > > > > Thanks > > Vivek > > No, I don't think thats necessecary. Once the apics are enabled, interrupts > shouldn't travel accross the hypertransport bus anyway, opting instead to use > the dedicated apic bus (at least thats my understanding). I think all interrupt message travel on hypertransport. Even after APICS have been enabled. Look at the following document. http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/24674.pdf Have a look at figure 1, figure 2 and section 3.4.2.2 and 3.4.2.3 That's a different thing that once IOAPIC has formed the vectored message, Hypertransport might not touch the destination field. Having said that, I am wondering what will happen if a system continues to operate the timer through IOAPIC in ExtInt mode. Will hypertransport keep on broadcasting that interrupt to every cpu? And every cpu will process that interrupt. Hence, I feel it is safe to restore the broadcast bit back to BIOS value once we are through calibrate_delay(). Thanks Vivek
