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Subject[RFC] linux-2.4.20-pre2_tsc-disable_B11
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Hi Alan, 
Just wanted to pass this by you quickly. First, forgive me: internally
we were having some problems with the last version of this patch that I
posted so I've been too busy hunting down the problem to include the
timer.c cleanups we discussed or sync it up w/ your tree.

The problem is that with my patch on a summit based box, when
HyperThreading is disabled in the BIOS, the io_apic code bugs out when
calling timer_irq_works(). Ends up that after calling "mdelay((10 *
1000) / HZ);" we return and only 4 ticks have passed.

My suspicion is that when HT is disabled, the processor is less busy
switching between threads. Thus calls to mdelay(), which calls
__loop_delay() with my patch, execute faster then they should.

However, I'm at a bit of a loss, because when HT is enabled, the CPUs
BogoMIPS (thus loops_per_jiffy) drops. This should mean when HT is off,
loops_per_jiffy should be larger, and thus mdelay should take longer.
Looking through the calibrate_delay and mdelay code I can't see anything
that seems off.

Anyway, my options to "just make it work" seem to be:

1) Use the unsynced TSC for udelay.
2) Just increase the time we wait in the io_apic code.

Since the first method breaks on multi-frequency SMP boxes, and is
totally broken with preempt, I opted for #2. While its not very
scientific, I'm not sure how much it matters, as the ioapic is just
checking to make sure the timer interrupt is working. Although I could
be totally wrong.

Anyway, just wanted to mail you the patch and ask for comments as to
what you or anyone else might think the proper fix is.

thanks
-john


diff -Nru a/Documentation/Configure.help b/Documentation/Configure.help
--- a/Documentation/Configure.help Wed Aug 14 19:14:10 2002
+++ b/Documentation/Configure.help Wed Aug 14 19:14:10 2002
@@ -230,7 +230,21 @@
network and embedded applications. For more information see the
Axis Communication site, <http://developer.axis.com/>.

-Multiquad support for NUMA systems
+Multi-node support for NUMA systems
+CONFIG_X86_NUMA
+ This option is used for getting Linux to run on a NUMA multi-node box.
+ Because multi-node systems suffer from unsynced TSCs, as well as TSC
+ drift, which can cause gettimeofday to return non-monotonic values,
+ this option will turn off the CONFIG_X86_TSC optimization. This
+ allows you to then specify "badtsc" as a boot option to force all nodes
+ to use the PIT for gettimeofday.
+
+ Note: This does not disable access to the unsynced TSCs from userspace,
+ thus applications using the rdtsc instruction for timing may have
+ issues. To disable userspace access, instead of "badtsc" use the
+ "notsc" boot option.
+
+Multiquad support for NUMAQ systems
CONFIG_MULTIQUAD
This option is used for getting Linux to run on a (IBM/Sequent) NUMA
multiquad box. This changes the way that processors are bootstrapped,
diff -Nru a/arch/i386/config.in b/arch/i386/config.in
--- a/arch/i386/config.in Wed Aug 14 19:14:10 2002
+++ b/arch/i386/config.in Wed Aug 14 19:14:10 2002
@@ -82,7 +82,7 @@
define_int CONFIG_X86_L1_CACHE_SHIFT 5
define_bool CONFIG_X86_USE_STRING_486 y
define_bool CONFIG_X86_ALIGNMENT_16 y
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_PPRO_FENCE y
define_bool CONFIG_X86_F00F_WORKS_OK n
fi
@@ -90,14 +90,14 @@
define_int CONFIG_X86_L1_CACHE_SHIFT 5
define_bool CONFIG_X86_USE_STRING_486 y
define_bool CONFIG_X86_ALIGNMENT_16 y
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_GOOD_APIC y
define_bool CONFIG_X86_PPRO_FENCE y
define_bool CONFIG_X86_F00F_WORKS_OK n
fi
if [ "$CONFIG_M686" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_GOOD_APIC y
define_bool CONFIG_X86_PGE y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
@@ -106,7 +106,7 @@
fi
if [ "$CONFIG_MPENTIUMIII" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_GOOD_APIC y
define_bool CONFIG_X86_PGE y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
@@ -114,7 +114,7 @@
fi
if [ "$CONFIG_MPENTIUM4" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 7
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_GOOD_APIC y
define_bool CONFIG_X86_PGE y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
@@ -123,12 +123,12 @@
if [ "$CONFIG_MK6" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
define_bool CONFIG_X86_ALIGNMENT_16 y
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
fi
if [ "$CONFIG_MK7" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 6
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_GOOD_APIC y
define_bool CONFIG_X86_USE_3DNOW y
define_bool CONFIG_X86_PGE y
@@ -143,14 +143,14 @@
fi
if [ "$CONFIG_MCYRIXIII" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_ALIGNMENT_16 y
define_bool CONFIG_X86_USE_3DNOW y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
fi
if [ "$CONFIG_MCRUSOE" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_F00F_WORKS_OK y
fi
if [ "$CONFIG_MWINCHIPC6" = "y" ]; then
@@ -163,7 +163,7 @@
if [ "$CONFIG_MWINCHIP2" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
define_bool CONFIG_X86_ALIGNMENT_16 y
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
define_bool CONFIG_X86_OOSTORE y
define_bool CONFIG_X86_F00F_WORKS_OK y
@@ -171,7 +171,7 @@
if [ "$CONFIG_MWINCHIP3D" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
define_bool CONFIG_X86_ALIGNMENT_16 y
- define_bool CONFIG_X86_TSC y
+ define_bool CONFIG_X86_HAS_TSC y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
define_bool CONFIG_X86_OOSTORE y
define_bool CONFIG_X86_F00F_WORKS_OK y
@@ -216,8 +216,17 @@
define_bool CONFIG_X86_IO_APIC y
fi
else
- bool 'Multiquad NUMA system' CONFIG_MULTIQUAD
+ bool 'Multi-node NUMA system support' CONFIG_X86_NUMA
+ if [ "$CONFIG_X86_NUMA" = "y" ]; then
+ bool ' Multiquad (IBM/Sequent) NUMAQ support' CONFIG_MULTIQUAD
+ fi
fi
+
+if [ "$CONFIG_X86_NUMA" != "y" -a "$CONFIG_X86_HAS_TSC" = "y" ]; then
+ define_bool CONFIG_X86_TSC y
+fi
+
+bool 'ISA bus support' CONFIG_ISA

if [ "$CONFIG_SMP" = "y" -a "$CONFIG_X86_CMPXCHG" = "y" ]; then
define_bool CONFIG_HAVE_DEC_LOCK y
diff -Nru a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
--- a/arch/i386/kernel/io_apic.c Wed Aug 14 19:14:10 2002
+++ b/arch/i386/kernel/io_apic.c Wed Aug 14 19:14:10 2002
@@ -1141,8 +1141,8 @@
unsigned int t1 = jiffies;

sti();
- /* Let ten ticks pass... */
- mdelay((10 * 1000) / HZ);
+ /* Let fifteen ticks pass... */
+ mdelay((15 * 1000) / HZ);

/*
* Expect a few ticks at least, to be sure some possible
diff -Nru a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
--- a/arch/i386/kernel/time.c Wed Aug 14 19:14:10 2002
+++ b/arch/i386/kernel/time.c Wed Aug 14 19:14:10 2002
@@ -69,6 +69,9 @@
/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;

+/*boot option flag to keep gettimeofday from using do_fastgettimeoffset */
+static int bad_tsc __initdata = 0;
+
static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */

/* Cached *multiplier* to convert TSC counts to microseconds.
@@ -634,6 +637,16 @@
return 0;
}

+/* badtsc boot option: Used to keep do_gettimeofday from
+ * using do_fast_gettimeoffset()
+ */
+static int __init bad_tsc_setup(char *str)
+{
+ bad_tsc = 1;
+ return 1;
+}
+__setup("badtsc", bad_tsc_setup);
+
void __init time_init(void)
{
extern int x86_udelay_tsc;
@@ -672,16 +685,17 @@
unsigned long tsc_quotient = calibrate_tsc();
if (tsc_quotient) {
fast_gettimeoffset_quotient = tsc_quotient;
- use_tsc = 1;
/*
* We could be more selective here I suspect
* and just enable this for the next intel chips ?
*/
- x86_udelay_tsc = 1;
+ if(!bad_tsc){
+ use_tsc = 1;
+ x86_udelay_tsc = 1;
#ifndef do_gettimeoffset
- do_gettimeoffset = do_fast_gettimeoffset;
+ do_gettimeoffset = do_fast_gettimeoffset;
#endif
-
+ }
/* report CPU clock rate in Hz.
* The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
* clock/second. Our precision is about 100 ppm.
-
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