gorcunov at gmail
Jul 12, 2008, 12:22 AM
Post #3 of 6
(116 views)
Permalink
|
|
Re: [PATCH -tip] x86: apic LVTT - use APIC_DIVISOR on 64bit mode
[In reply to]
|
|
[Ingo Molnar - Sat, Jul 12, 2008 at 08:05:04AM +0200]
|
| * Cyrill Gorcunov <gorcunov[at]gmail.com> wrote:
|
| > We use APIC_TDR_DIV_16 while setting APIC_TDCR (divisor) it happened
| > this moment is hidden from __setup_APIC_LVTT caller. So we better
| > increment caller 'clocks' value to not change current behaviour and
| > use APIC_DIVISOR (as already done in 32bit version).
| >
| > The main benefit - unified procedure code for 32/64bit modes.
|
| > Please review carefully. Any comments are welcome.
| > I'm _not_ 100% sure if this patch is safe.
|
| hm, how about the other caller to __setup_APIC_LVTT(),
| lapic_timer_setup():
|
| case CLOCK_EVT_MODE_ONESHOT:
| __setup_APIC_LVTT(calibration_result,
| mode != CLOCK_EVT_MODE_PERIODIC, 1);
| break;
|
| that will affect high-res timers. Wont calibration_result have the same
| value after your patch as well, but only a 16th of it will be used in
| __setup_APIC_LVTT(), causing 16 times shorter timeouts than intended?
|
| I.e. are we fixing a bug, are we changing nothing, or are we introducing
| a bug? :-)
|
| Ingo
|
well, the last I would say :). That happened I sent first version of
patch instead of modified second version. Thanks a lot Ingo for catching
it! Oh my, sorry... Here is an updated version.
---
We use APIC_TDR_DIV_16 while setting APIC_TDCR (divisor).
It happened this moment is hidden from __setup_APIC_LVTT
caller. So we better increment caller 'clocks' value to
not change current behaviour and use APIC_DIVISOR
(as already done in 32bit version).
The main benefit - unified procedure code for 32/64bit modes.
Signed-off-by: Cyrill Gorcunov <gorcunov[at]gmail.com>
CC: "Maciej W. Rozycki" <macro[at]linux-mips.org>
---
Index: linux-2.6.git/arch/x86/kernel/apic_64.c
===================================================================
--- linux-2.6.git.orig/arch/x86/kernel/apic_64.c 2008-07-12 11:11:33.000000000 +0400
+++ linux-2.6.git/arch/x86/kernel/apic_64.c 2008-07-12 11:14:22.000000000 +0400
@@ -165,6 +165,9 @@ int lapic_get_maxlvt(void)
return maxlvt;
}
+/* Clock divisor is set to 16 */
+#define APIC_DIVISOR 16
+
/*
* This function sets up the local APIC timer, with a timeout of
* 'clocks' APIC bus clock. During calibration we actually call
@@ -197,7 +200,7 @@ static void __setup_APIC_LVTT(unsigned i
| APIC_TDR_DIV_16);
if (!oneshot)
- apic_write(APIC_TMICT, clocks);
+ apic_write(APIC_TMICT, clocks/APIC_DIVISOR);
}
/*
@@ -329,7 +332,7 @@ static void __init calibrate_APIC_clock(
*
* No interrupt enable !
*/
- __setup_APIC_LVTT(250000000, 0, 0);
+ __setup_APIC_LVTT(4000000000, 0, 0);
apic_start = apic_read(APIC_TMCCT);
#ifdef CONFIG_X86_PM_TIMER
@@ -367,7 +370,7 @@ static void __init calibrate_APIC_clock(
lapic_clockevent.min_delta_ns =
clockevent_delta2ns(0xF, &lapic_clockevent);
- calibration_result = result / HZ;
+ calibration_result = result * APIC_DIVISOR / HZ;
}
/*
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo[at]vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
|
