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Add a new test_counter() function which tries to determine the width of

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the inter-value histogram for 2000 samples.  If the width is 3 or less
for 10 consequtive samples, we trust the counter to be good, otherwise
we use the *_safe() method.

This method may be too strict, but the worst which can happen is that
we take the performance hit of the *_safe() method when we should not.

Make the *_safe() method more discriminating by mandating that the three
samples do not span more than 15 ticks on the counter.

Disable the PCI-ident based probing as a means to recognize good
counters.

Inspiration from:	dillon and msmith
This commit is contained in:
Poul-Henning Kamp 2002-02-25 09:51:17 +00:00
parent 6d53e16389
commit cb877d0050
1 changed files with 46 additions and 17 deletions
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63
sys/dev/acpica/acpi_timer.c
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@ -104,6 +104,38 @@ static struct timecounter acpi_timer_timecounter = {
SYSCTL_OPAQUE(_debug, OID_AUTO, acpi_timecounter, CTLFLAG_RD,
&acpi_timer_timecounter, sizeof(acpi_timer_timecounter), "S,timecounter", "");
static int test_counter(void);
#define N 2000
static int
test_counter()
{
int min, max, n, delta;
unsigned last, this;
min = 10000000;
max = 0;
last = TIMER_READ;
for (n = 0; n < N; n++) {
this = TIMER_READ;
delta = (this - last) & 0xffffff;
if (delta > max)
max = delta;
else if (delta < min)
min = delta;
last = this;
}
if (max - min > 2)
n = 0;
else if (min < 0)
n = 0;
else
n = 1;
printf("ACPI timer looks %s min = %d, max = %d, width = %d\n",
n ? "GOOD" : "BAD ",
min, max, max - min + 1);
return (n);
}
/*
* Locate the ACPI timer using the FADT, set up and allocate the I/O resources
@ -114,7 +146,7 @@ acpi_timer_identify(driver_t *driver, device_t parent)
{
device_t dev;
char desc[40];
int rid;
int rid, i, j;
ACPI_FUNCTION_TRACE(__func__);
@ -138,27 +170,22 @@ acpi_timer_identify(driver_t *driver, device_t parent)
if (getenv("debug.acpi.timer_test") != NULL)
acpi_timer_test();
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
acpi_timer_timecounter.tc_frequency = acpi_timer_frequency;
j = 0;
for(i = 0; i < 10; i++)
j += test_counter();
if (j == 10) {
acpi_timer_timecounter.tc_name = "ACPI-fast";
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
} else {
acpi_timer_timecounter.tc_name = "ACPI-safe";
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
}
tc_init(&acpi_timer_timecounter);
sprintf(desc, "%d-bit timer at 3.579545MHz", AcpiGbl_FADT->TmrValExt ? 32 : 24);
device_set_desc_copy(dev, desc);
#if 0
{
u_int64_t first;
first = rdtsc();
acpi_timer_get_timecount(NULL);
printf("acpi_timer_get_timecount %lld cycles\n", rdtsc() - first);
first = rdtsc();
acpi_timer_get_timecount_safe(NULL);
printf("acpi_timer_get_timecount_safe %lld cycles\n", rdtsc() - first);
}
#endif
return_VOID;
}
@ -200,7 +227,7 @@ acpi_timer_get_timecount_safe(struct timecounter *tc)
u1 = u2;
u2 = u3;
u3 = TIMER_READ;
} while (u1 > u2 || u2 > u3);
} while (u1 > u2 || u2 > u3 || (u3 - u1) > 15);
return (u2);
}
@ -293,6 +320,7 @@ acpi_timer_test(void)
* directions. If we only cared about monosity two reads would be enough.
*/
#if 0
static int acpi_timer_pci_probe(device_t dev);
static device_method_t acpi_timer_pci_methods[] = {
@ -335,3 +363,4 @@ acpi_timer_pci_probe(device_t dev)
return(ENXIO); /* we never match anything */
}
#endif