Date: Mon, 06 Feb 2006 20:29:35 -0800 From: Cy Schubert <Cy.Schubert@komquats.com> To: freebsd-current@freebsd.org, netchild@freebsd.org Subject: Re: 7.0-CURRENT Hang Message-ID: <200602070429.k174TZ6v009581@cwsys.cwsent.com>
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Oops. In my haste I made a typo in my note. It should read when AL = 0x02.
It should read as follows:
I identified the problem (see my original discussion about this in attached
the email below).
On the Pentium P54C model (that's an old 120 MHz Pentium I use as a 4.x,
5.x, and 7.x ports build testbed) the CPUID instruction when called with AL
= 0x02, CPUID returns EAX = EBX = ECX = EDX = 0. The code fragment in
identcpu.c below results in "rounds" becoming 0xffffffff.
do_cpuid(0x2, regs);
rounds = (regs[0] & 0xff) - 1;
The subsequent loop of the following will loop virtually for ever (it takes
forever tor this machine to count down from 0xffffffff performing a very
great many calls to get_INTEL_TLB in the process, virtually hanging the
machine in the process.
while (rounds > 0) {
[... code ...]
rounds--;
}
To resolve my problem I cobbled up the following patch to identcpu.c:
--- sys/i386/i386/identcpu.c.orig Thu Feb 2 04:44:09 2006
+++ sys/i386/i386/identcpu.c Mon Feb 6 18:47:16 2006
@@ -1237,7 +1237,7 @@
do_cpuid(0x2, regs);
- rounds = (regs[0] & 0xff) - 1;
+ rounds = (regs[0] & 0xff);
for (regnum = 0; regnum <= 3; ++regnum) {
if ((regs[regnum] & (1<<31)) == 0) {
@@ -1249,7 +1249,7 @@
}
}
- while (rounds > 0) {
+ while (rounds > 1) {
do_cpuid(0x2, regs);
for (regnum = 0; regnum <= 3; ++regnum) {
@@ -1452,7 +1452,7 @@
u_int nwaycode;
do_cpuid(0x2, regs);
- rounds = (regs[0] & 0xff) - 1;
+ rounds = (regs[0] & 0xff);
for (regnum = 0; regnum <= 3; ++regnum) {
if ((regs[regnum] & (1<<31)) == 0) {
@@ -1468,7 +1468,7 @@
}
}
- while (rounds > 0) {
+ while (rounds > 1) {
do_cpuid(0x2, regs);
for (regnum = 0; regnum <= 3; ++regnum) {
It fixes the hang.
Cheers,
Cy Schubert <Cy.Schubert@komquats.com>
Web: http://www.komquats.com and http://www.bcbodybuilder.com
FreeBSD UNIX: <cy@FreeBSD.org> Web: http://www.FreeBSD.org
BC Government: <Cy.Schubert@gov.bc.ca>
"Lift long enough and I believe arrogance is replaced by
humility and fear by courage and selfishness by generosity
and rudeness by compassion and caring."
-- Dave Draper
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