Re: [PATCH] 2.6.17-rt add clockevent to ixp4xx
From: Kevin Hilman
Date: Thu Jul 13 2006 - 17:46:30 EST
On Thu, 2006-07-13 at 10:53 +0000, Milan Svoboda wrote:
> there are patches that enable clock event on ixp4xx platform. This should
> enable high resolution timers... Option for hrtimers in menuconfig is
> also enabled.
Milan,
I've also done a clockevent driver for ixp4xx and it looks pretty much
like yours. I've been waiting to submit as Thomas has recently reworked
the clockevent layer a bit in his -hrt-dyntick patchset.
Here are a couple comments on your patchset
- since you've registered the clockevent with CAP_TICK, both the
arch interrupt handler and the clockevent handler are handling the tick
and calling do_timer(). While I don't think this will negatively affect
timekeeping, it's unncessary overhead.
- why the addition of clockevent_hz2mult()? since shift is 32, you
could use existing div_sc32()
The attached patch is a combination of my patch and yours and addresses
my comments above. I simply removed the CLOCK_CAP_TICK and removed your
clockevent_hz2mult() and used div_sc32().
Also, below are a few runs of the nanosleep_jitter test that comes with
the sourceforge HRT test suite. Something strange is that with the
nanosleep_jitter test, I only see max sleeps of ~300-400 usec but with
your test I see max sleeps up to 1.3 msec.
Kevin
root@ixp425:/kjh# gcc -DCLOCK_REALTIME_HR=CLOCK_REALTIME
nanosleep_jitter.c -lposixtime
root@ixp425:/kjh# ./a.out
Doing 10 iterations of sleeping for 50 micro seconds 1000 times
Total time for each iteration should be 0.050000 seconds.
Iteration iter time (secs) min sleep max sleep
0 0.075580 0.075575 0.000075 0.000084
1 0.075526 0.075521 0.000074 0.000082
2 0.075529 0.075525 0.000074 0.000082
3 0.075518 0.075514 0.000074 0.000082
4 0.075526 0.075521 0.000075 0.000082
5 0.075525 0.075521 0.000074 0.000082
6 0.075526 0.075521 0.000074 0.000082
7 0.075519 0.075514 0.000074 0.000082
8 0.075526 0.075522 0.000075 0.000082
9 0.244572 0.244564 0.000074 0.000316
root@ixp425:/kjh# ./a.out
Doing 10 iterations of sleeping for 50 micro seconds 1000 times
Total time for each iteration should be 0.050000 seconds.
Iteration iter time (secs) min sleep max sleep
0 0.075644 0.075639 0.000075 0.000083
1 0.075527 0.075523 0.000075 0.000082
2 0.075518 0.075514 0.000074 0.000082
3 0.075525 0.075521 0.000075 0.000082
4 0.075530 0.075525 0.000074 0.000082
5 0.075526 0.075521 0.000074 0.000082
6 0.075518 0.075514 0.000074 0.000082
7 0.075526 0.075521 0.000075 0.000082
8 0.075526 0.075521 0.000074 0.000082
9 0.147196 0.147187 0.000074 0.000311
root@ixp425:/kjh# ./a.out
Doing 10 iterations of sleeping for 50 micro seconds 1000 times
Total time for each iteration should be 0.050000 seconds.
Iteration iter time (secs) min sleep max sleep
0 0.075588 0.075583 0.000075 0.000084
1 0.075534 0.075529 0.000074 0.000082
2 0.075537 0.075533 0.000074 0.000082
3 0.075526 0.075522 0.000074 0.000082
4 0.075533 0.075529 0.000075 0.000082
5 0.075533 0.075529 0.000074 0.000082
6 0.075594 0.075589 0.000074 0.000083
7 0.075540 0.075535 0.000074 0.000086
8 0.075539 0.075534 0.000075 0.000084
9 0.075527 0.075522 0.000074 0.000083
root@ixp425:/kjh#
ARM: Add HRT clockevent support for IXP4xx platform
Signed-off-by: Milan Svoboda <msvoboda@xxxxxxxxxxxxxxx>
Signed-off-by: Kevin Hilman <khilman@xxxxxxxxxxxxxx>
Index: ixp4xx/arch/arm/mach-ixp4xx/common.c
===================================================================
--- ixp4xx.orig/arch/arm/mach-ixp4xx/common.c
+++ ixp4xx/arch/arm/mach-ixp4xx/common.c
@@ -28,6 +28,7 @@
#include <linux/time.h>
#include <linux/timex.h>
#include <linux/clocksource.h>
+#include <linux/clockchips.h>
#include <asm/hardware.h>
#include <asm/uaccess.h>
@@ -256,15 +257,31 @@ void __init ixp4xx_init_irq(void)
static unsigned volatile last_jiffy_time;
-#define CLOCK_TICKS_PER_USEC ((CLOCK_TICK_RATE + USEC_PER_SEC/2) / USEC_PER_SEC)
+#ifdef CONFIG_HIGH_RES_TIMERS
+static void ixp4xx_set_next_event(unsigned long evt, void *priv)
+{
+ *IXP4XX_OSRT1 = (evt & ~IXP4XX_OST_RELOAD_MASK) | IXP4XX_OST_ENABLE;
+}
+
+static struct clock_event clockevent_ixp4xx = {
+ .name = "OSTS clock event interface",
+ .capabilities = CLOCK_CAP_NEXTEVT | CLOCK_HAS_IRQHANDLER,
+ .shift = 32,
+ .set_next_event = ixp4xx_set_next_event,
+};
+#endif
static irqreturn_t ixp4xx_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
- write_seqlock(&xtime_lock);
-
/* Clear Pending Interrupt by writing '1' to it */
*IXP4XX_OSST = IXP4XX_OSST_TIMER_1_PEND;
+#ifdef CONFIG_HIGH_RES_TIMERS
+ if (clockevent_ixp4xx.event_handler)
+ clockevent_ixp4xx.event_handler(regs, NULL);
+#endif
+ write_seqlock(&xtime_lock);
+
/*
* Catch up with the real idea of time
*/
@@ -404,7 +421,7 @@ static struct clocksource clocksource_ix
.rating = 200,
.read = ixp4xx_get_cycles,
.mask = 0xFFFFFFFF,
- .shift = 10,
+ .shift = 20,
.is_continuous = 1,
};
@@ -419,5 +436,19 @@ static int __init ixp4xx_clocksource_ini
return 0;
}
-
device_initcall(ixp4xx_clocksource_init);
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+static int __init ixp4xx_clockevent_init(void)
+{
+ clockevent_ixp4xx.mult = div_sc32(FREQ, NSEC_PER_SEC);
+ clockevent_ixp4xx.max_delta_ns =
+ clockevent_delta2ns(0xfffffffe, &clockevent_ixp4xx);
+ clockevent_ixp4xx.min_delta_ns =
+ clockevent_delta2ns(0xf, &clockevent_ixp4xx);
+ setup_local_clockevent(&clockevent_ixp4xx, CPU_MASK_NONE);
+
+ return 0;
+}
+device_initcall(ixp4xx_clockevent_init);
+#endif