Messages in this thread | | | Date | Sun, 13 Jul 2008 20:23:37 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [RFC] lapic calibration results fix |
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[Cyrill Gorcunov - Sun, Jul 13, 2008 at 03:37:34PM +0400] | Ingo, Maciej, | | it seems I found a bit strange code snippet in apic_32.c:setup_boot_APIC_clock. | We set local_apic_timer_verify_ok = 1 before checking the results. I think | the following patch make sense. Please take a look on. | | --- | We set lapic flag that clocksource calibration is | fine too early. Fix it. | | Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com> | --- | | Index: linux-2.6.git/arch/x86/kernel/apic_32.c | =================================================================== | --- linux-2.6.git.orig/arch/x86/kernel/apic_32.c 2008-07-13 15:25:20.000000000 +0400 | +++ linux-2.6.git/arch/x86/kernel/apic_32.c 2008-07-13 15:31:03.000000000 +0400 | @@ -489,8 +489,6 @@ void __init setup_boot_APIC_clock(void) | calibration_result / (1000000 / HZ), | calibration_result % (1000000 / HZ)); | | - local_apic_timer_verify_ok = 1; | - | /* | * Do a sanity check on the APIC calibration result | */ | @@ -504,6 +502,8 @@ void __init setup_boot_APIC_clock(void) | return; | } | | + local_apic_timer_verify_ok = 1; | + | /* We trust the pm timer based calibration */ | if (!pm_referenced) { | apic_printk(APIC_VERBOSE, "... verify APIC timer\n");
Letme clarify a bit situation why I propose this path (it's not that clear from its description).
While calibrating apic timer we use different 'flags' signaling if it was success/fail. On 64bit platform lapic_timer_setup() does check for CLOCK_EVT_FEAT_DUMMY bit which is set by default and cleared on successfully calibrated timer. So 64bit is fine now. On 32bit we use a different approach - local_apic_timer_verify_ok flag _BUT_ as I see it being set too early _before_ calibration result is checked so we could have the following - kernel reports user that APIC timer is too slow and disabled but local_apic_timer_verify_ok remains set to 1 instead of 0.
- Cyrill -
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