Date: Mon, 18 Feb 2002 14:07:57 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Mike Smith <msmith@hub.freebsd.org>, John Polstra <jdp@polstra.com>, hackers@FreeBSD.ORG Subject: Re: ACPI timecounter tests original fast version vs masked version Message-ID: <200202182207.g1IM7v055546@apollo.backplane.com> References: <45878.1014065298@critter.freebsd.dk>
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:My only worry here is laptops.
:
:If my laptop is connected to the wall-power when it boots it comes
:up at full CPU speed during the probe and mask determination.
:
:Then I unplug it and the CPU speed drops by a large factor and
:suddenly the mask is too tight for the CPU to get two samples.
:
:I think we need an approach where we loosen the mask at runtime if
:some significant number of iterations fail to get a count may be
:needed:
:
:#define N 25
:
: static unsigned mask = 0xfffffffe;
:
: for (;;) {
: for (i = 0; i < N; i++) {
: c = READ_TIMER & mask;
: d = READ_TIMER & mask;
: if (c == d)
: return(d);
: }
: printf("Adjusting mask to %08x\n", mask);
: mask <<= 1;
: }
:
:
:--
:Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
:phk@FreeBSD.ORG | TCP/IP since RFC 956
Ok, try this patch. It will do fallback but does not do fallforward,
and performance should be improved for the best case. I also put
the mask in a _debug sysctl so you can play with it. Be careful,
you can blow up the time counter if you set it to a bad value like 0
reasonable values: -1, -2, -4, -8, -16, -32, -64. If you set it too
strict (i.e. -1) it will auto fallback.
-Matt
Matthew Dillon
<dillon@backplane.com>
Index: acpi_timer.c
===================================================================
RCS file: /home/ncvs/src/sys/dev/acpica/acpi_timer.c,v
retrieving revision 1.11
diff -u -r1.11 acpi_timer.c
--- acpi_timer.c 8 Jan 2002 06:45:56 -0000 1.11
+++ acpi_timer.c 18 Feb 2002 22:02:55 -0000
@@ -56,11 +56,17 @@
MODULE_NAME("TIMER")
static device_t acpi_timer_dev;
+static u_int32_t acpi_timer_mask;
struct resource *acpi_timer_reg;
#define TIMER_READ bus_space_read_4(rman_get_bustag(acpi_timer_reg), \
rman_get_bushandle(acpi_timer_reg), \
0)
+/*
+ * Loops before we give up and recalculate the mask
+ */
+#define NLOOP 32 /* power of 2 */
+
static u_int acpi_timer_frequency = 14318182/4;
static void acpi_timer_identify(driver_t *driver, device_t parent);
@@ -70,6 +76,7 @@
static unsigned acpi_timer_get_timecount_safe(struct timecounter *tc);
static int acpi_timer_sysctl_freq(SYSCTL_HANDLER_ARGS);
static void acpi_timer_test(void);
+static void calc_acpi_timer_mask(void);
/*
* Driver hung off ACPI.
@@ -102,6 +109,7 @@
"ACPI"
};
+SYSCTL_INT(_debug, OID_AUTO, acpi_timer_mask, CTLFLAG_RW, &acpi_timer_mask, 0, "");
SYSCTL_OPAQUE(_debug, OID_AUTO, acpi_timecounter, CTLFLAG_RD,
&acpi_timer_timecounter, sizeof(acpi_timer_timecounter), "S,timecounter", "");
@@ -113,7 +121,7 @@
acpi_timer_identify(driver_t *driver, device_t parent)
{
device_t dev;
- char desc[40];
+ char desc[48];
int rid;
FUNCTION_TRACE(__func__);
@@ -138,14 +146,17 @@
if (getenv("debug.acpi.timer_test") != NULL)
acpi_timer_test();
- acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
+ acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
acpi_timer_timecounter.tc_frequency = acpi_timer_frequency;
tc_init(&acpi_timer_timecounter);
- sprintf(desc, "%d-bit timer at 3.579545MHz", AcpiGbl_FADT->TmrValExt ? 32 : 24);
+ calc_acpi_timer_mask();
+
+ sprintf(desc, "%d-bit timer at 3.579545MHz mask %08x",
+ (AcpiGbl_FADT->TmrValExt ? 32 : 24), acpi_timer_mask);
device_set_desc_copy(dev, desc);
-#if 0
+#if 0
{
u_int64_t first;
@@ -162,6 +173,32 @@
return_VOID;
}
+static
+void
+calc_acpi_timer_mask(void)
+{
+ u_int32_t mask;
+
+ critical_enter();
+ for (mask = 0xFFFFFFFF; mask; mask <<= 1) {
+ u_int32_t u1;
+ u_int32_t u2;
+ int count = NLOOP;
+
+ u1 = TIMER_READ;
+ u2 = TIMER_READ;
+ while (count && ((u1 ^ u2) & mask)) {
+ u1 = u2;
+ u2 = TIMER_READ;
+ --count;
+ }
+ if (count)
+ break;
+ }
+ critical_exit();
+ acpi_timer_mask = mask << 1;
+}
+
static int
acpi_timer_probe(device_t dev)
{
@@ -192,16 +229,32 @@
static unsigned
acpi_timer_get_timecount_safe(struct timecounter *tc)
{
- unsigned u1, u2, u3;
+ u_int32_t u1;
+ u_int32_t u2;
+ int n;
+
+ u1 = TIMER_READ & acpi_timer_mask;
+ u2 = TIMER_READ & acpi_timer_mask;
+ if (u1 == u2)
+ return(u2);
+ u1 = u2;
+ u2 = TIMER_READ & acpi_timer_mask;
+ if (u1 == u2)
+ return(u2);
- u2 = TIMER_READ;
- u3 = TIMER_READ;
- do {
+ n = 0;
+ for (;;) {
u1 = u2;
- u2 = u3;
- u3 = TIMER_READ;
- } while (u1 > u2 || u2 > u3);
- return (u2);
+ u2 = TIMER_READ & acpi_timer_mask;
+ if (u1 == u2)
+ break;
+ ++n;
+ if ((n & (NLOOP - 1)) == 0) {
+ calc_acpi_timer_mask();
+ u2 = TIMER_READ & acpi_timer_mask;
+ }
+ }
+ return(u2);
}
/*
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