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Date: Fri, 08 Jan 2010 12:42:37 -0500 From: Mark Hounschell <markh@...pro.net> To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> CC: Andi Kleen <andi@...stfloor.org>, Linus Torvalds <torvalds@...ux-foundation.org>, "dmarkh@....rr.com" <dmarkh@....rr.com>, Alain Knaff <alain@...ff.lu>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "fdutils@...tils.linux.lu" <fdutils@...tils.linux.lu>, "Li, Shaohua" <shaohua.li@...el.com>, Ingo Molnar <mingo@...e.hu> Subject: Re: [Fdutils] DMA cache consistency bug introduced in 2.6.28 On 12/23/2009 03:30 PM, Pallipadi, Venkatesh wrote: >>> Can you try this one line patch either on .28 or .32 (with /proc/interrupts >>> output). >>> This disables hpet2 and lapic timer should then be used on CPU 0. If things >>> work with this test patch, we will know that the failure is somehow related >>> to HPET usage in MSI mode. >>> >>> Thanks, >>> Venki >>> >>> Reduce the rating of percpu hpet timer >>> >>> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com> >>> --- >>> arch/x86/kernel/hpet.c | 2 +- >>> 1 files changed, 1 insertions(+), 1 deletions(-) >>> >>> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c >>> index cafb1c6..f89d17a 100644 >>> --- a/arch/x86/kernel/hpet.c >>> +++ b/arch/x86/kernel/hpet.c >>> @@ -480,7 +480,7 @@ static void init_one_hpet_msi_clockevent(struct hpet_dev *hdev, int cpu) >>> hpet_setup_irq(hdev); >>> evt->irq = hdev->irq; >>> >>> - evt->rating = 110; >>> + evt->rating = 40; >>> evt->features = CLOCK_EVT_FEAT_ONESHOT; >>> if (hdev->flags & HPET_DEV_PERI_CAP) >>> evt->features |= CLOCK_EVT_FEAT_PERIODIC; >> >> That made it work. Used 2.6.32.2 >> >> cat /proc/interrupts >> CPU0 CPU1 CPU2 CPU3 >> 0: 82 0 0 1 IO-APIC-edge timer >> 1: 0 0 0 67 IO-APIC-edge i8042 >> 3: 0 0 0 6 IO-APIC-edge >> 4: 0 0 0 4 IO-APIC-edge >> 6: 0 0 0 4 IO-APIC-edge floppy >> 8: 0 0 0 8 IO-APIC-edge rtc0 >> 9: 0 0 0 0 IO-APIC-fasteoi acpi >> 12: 0 0 10 1519 IO-APIC-edge i8042 >> 14: 0 0 39 10995 IO-APIC-edge >> pata_atiixp >> 15: 0 0 3 391 IO-APIC-edge >> pata_atiixp >> 16: 0 0 2 606 IO-APIC-fasteoi >> aic79xx, ohci_hcd:usb3, ohci_hcd:usb4, HDA Intel, Digi DBX2, ni-pci-gpib >> 17: 0 0 0 3 IO-APIC-fasteoi >> ehci_hcd:usb1, parport0, ni-pci-gpib >> 18: 0 0 10 2168 IO-APIC-fasteoi >> ohci_hcd:usb5, ohci_hcd:usb6, ohci_hcd:usb7, Digi DBX2, nvidia >> 19: 0 0 0 130 IO-APIC-fasteoi >> aic7xxx, ehci_hcd:usb2, ttySLG0, eth1 >> 22: 0 0 8 1151 IO-APIC-fasteoi ahci >> 24: 0 0 0 0 HPET_MSI-edge hpet2 >> 29: 0 0 0 48 PCI-MSI-edge >> sky2@pci:0000:04:00.0 >> NMI: 0 0 0 0 Non-maskable interrupts >> LOC: 34842 30177 29672 29632 Local timer interrupts >> SPU: 0 0 0 0 Spurious interrupts >> PMI: 0 0 0 0 Performance monitoring >> interrupts >> PND: 0 0 0 0 Performance pending work >> RES: 17501 20449 16670 11224 Rescheduling interrupts >> CAL: 10554 2336 1102 1071 Function call interrupts >> TLB: 364 562 753 468 TLB shootdowns >> ERR: 0 >> MIS: 0 >> >> >> # fdformat /dev/fd0u1440 >> Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB. >> Formatting ... done >> Verifying ... done > > Hmmm.. Thats very interesting indeed. > > That clearly says that HPET MSI interrupts somehow is causing some > caching side effect in the chipset that results in this floppy dma > failure. > > Here's is what we have until now. > IRQ 0 is based on HPET legacy interrupt and HPET device is also capable > of MSI on this platform. So we also have a percpu hpet (hpet2 tied to > CPU0). percpu hpet was added to avoid the usage of IRQ0+LAPIC broadcast > in cases where LAPIC timer will stop working in deep C-state. As we have > only one HPET channel free for percpu HPET, we only have hpet2 tied to > CPU 0 and other CPUs still have to go through IRQ0+LAPIC broadcast with > deep C-state. > > One problem here is that percpu hpet should only get used when LAPIC > cannot be used (that is when CPU enters deep C-state). Using hpet2 in > place of LAPIC timer even when deep C-state is not supported is not > right in terms of performance. We need some changes here to fix that > [Problem 1]. > > But, that still does not explain why we are seeing this problem in the > first place. I mean, using hpet2 is not optimal, but should not have > functionality issues like this. Even fixing [Problem 1] above, we may > see this problem on some other platform that supports deep C-state and > so has hpet2 enabled for a valid reason. > > Also, I am not sure whether the problem also happens if legacy HPET > interrupts are used during run time in place of LAPIC timer (May be > worth to try this with a simple test patch, let me think about it). In > this case, legacy HPET interrupt rightly goes quiet after boot, giving > priority to LAPIC timer. > > With hpet MSI interrupts, we do a write followed by read of HPET > memmapped register to set a HPET channel timeout + read of global HPET > timer. This happens on every timer interrupt on CPU 0. And we also have > MSI interrupt being delivered to CPU 0. I cannot think of any reason why > this can break dma. We can probably try adding some dummy HPET read > after dma write, to see if that flushes things properly. > Haven't seen any activity on this thread in a while. Just curious, are we still working this? Is there anything else I can do to help? Thanks Mark -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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