Messages in this thread Patch in this message | | | Date | Fri, 5 Nov 2010 17:09:19 +0100 | From | Borislav Petkov <> | Subject | Re: [bisected] Clocksource tsc unstable git |
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On Tue, Nov 02, 2010 at 11:26:54AM -0400, Thomas Gleixner wrote: > Ok, I'm waiting for Boris to get us the confirmation from HW folks.
Ok, I don't have much but it could be something. We could use the minimum tick u16 value in the ACPI HPET table, offset 53:
Main Counter Minimum 2 53 Unit: Clock tick Clock_tick in Periodic The minimum clock ticks can be set without lost Mode interrupts while the counter is programmed to operate in *Note#3 periodic mode
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* Note #3: This field is written by BIOS and may be chipset and/or platform dependent. This indicates the minimum value that must be used for any counter programmed in periodic mode to avoid lost interrupts. For any counter x that has been configured for periodic mode, the number can be programmed in any Tx_Compare Register must be greater than P, where P = (Minimum Period) / (Main counter period) in order to avoid lost interrupts.
However, we don't know (yet) whether this can be used in the non-periodic mode too. My gut feeling says yes but I wouldn't trust it.
We went and collected that value a bunch of systems and it looks like it would need more massaging (read: capping) since some BIOSen simply write crap in it. It ranges from
- 0x37ee on old nVidia and Intel boards (this is definitely crap, I can't imagine a minimum ticks value of 14318 for a HPET but who knows)
- 0x1000 on a HP machine (also fishy)
- 0x10, 0x14 on current SBxxx boards
- 0x80 on newer Intel boards
and it looks like 0x80 is also the default value which we can use as a capping value. Btw, I've been running the following on the machine in question for a while now and no lockups so far.
Opinions?
--- arch/x86/include/asm/hpet.h | 1 + arch/x86/kernel/acpi/boot.c | 12 +++++++++--- arch/x86/kernel/hpet.c | 3 ++- 3 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h index 2c392d6..01d9480 100644 --- a/arch/x86/include/asm/hpet.h +++ b/arch/x86/include/asm/hpet.h @@ -68,6 +68,7 @@ extern unsigned long force_hpet_address; extern u8 hpet_blockid; extern int hpet_force_user; extern u8 hpet_msi_disable; +extern u16 hpet_min_tick; extern int is_hpet_enabled(void); extern int hpet_enable(void); extern void hpet_disable(void); diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 71232b9..37b93e8 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -772,9 +772,6 @@ static int __init acpi_parse_hpet(struct acpi_table_header *table) hpet_address >>= 32; } #endif - printk(KERN_INFO PREFIX "HPET id: %#x base: %#lx\n", - hpet_tbl->id, hpet_address); - /* * Allocate and initialize the HPET firmware resource for adding into * the resource tree during the lateinit timeframe. @@ -790,6 +787,15 @@ static int __init acpi_parse_hpet(struct acpi_table_header *table) hpet_res->start = hpet_address; hpet_res->end = hpet_address + (1 * 1024) - 1; + hpet_min_tick = hpet_tbl->minimum_tick; + if (hpet_min_tick > 0x80) { + printk(KERN_WARNING PREFIX "Limiting HPET read delay to 0x80.\n"); + hpet_min_tick = 0x80; + } + + printk(KERN_INFO PREFIX "HPET id: %#x base: %#lx min tick: %d\n", + hpet_tbl->id, hpet_address, hpet_min_tick); + return 0; } diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index e49c3b9..a0b790a 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -40,6 +40,7 @@ u8 hpet_msi_disable; static unsigned long hpet_num_timers; #endif static void __iomem *hpet_virt_address; +u16 hpet_min_tick = 0x80; struct hpet_dev { struct clock_event_device evt; @@ -408,7 +409,7 @@ static int hpet_next_event(unsigned long delta, */ res = (s32)(cnt - hpet_readl(HPET_COUNTER)); - return res < 8 ? -ETIME : 0; + return res < hpet_min_tick ? -ETIME : 0; } static void hpet_legacy_set_mode(enum clock_event_mode mode, -- 1.7.3.1.50.g1e633
-- Regards/Gruss, Boris.
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