Date: Mon, 18 Feb 2002 13:36:20 -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: <200202182136.g1ILaKC42650@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
Ugh. Oh well. So much for the code being simple. I'll incorporate
a similar change which adjusts the mask dynamically in both directions.
-Matt
Matthew Dillon
<dillon@backplane.com>
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