Re: [patch?] s2ram + P4 + tsc = annoyance

From: Ingo Molnar
Date: Sun Dec 30 2007 - 09:10:38 EST


> ok, i prefer this fix a bit more. (we dont want to set last_tsc
> outside of the sync_lock - which your initial patch does)

i've added your patch to x86.git - thanks Mike! (patch below) I think
this would be too dangerous for v2.6.24 though - we can put it back into
-stable for 2.6.24.1, once it had more testing?

Ingo

----------------->
Subject: x86: fix: s2ram + P4 + tsc = annoyance
From: Mike Galbraith <efault@xxxxxx>

s2ram recently became useful here, except for the kernel's annoying
habit of disabling my P4's perfectly good TSC.

[ 107.894470] CPU 1 is now offline
[ 107.894474] SMP alternatives: switching to UP code
[ 107.895832] CPU0 attaching sched-domain:
[ 107.895836] domain 0: span 1
[ 107.895838] groups: 1
[ 107.896097] CPU1 is down
[ 3.726156] Intel machine check architecture supported.
[ 3.726165] Intel machine check reporting enabled on CPU#0.
[ 3.726167] CPU0: Intel P4/Xeon Extended MCE MSRs (12) available
[ 3.726170] CPU0: Thermal monitoring enabled
[ 3.726175] Back to C!
[ 3.726708] Force enabled HPET at resume
[ 3.726775] Enabling non-boot CPUs ...
[ 3.727049] CPU0 attaching NULL sched-domain.
[ 3.727165] SMP alternatives: switching to SMP code
[ 3.727858] Booting processor 1/1 eip 3000
[ 3.727862] CPU 1 irqstacks, hard=b042f000 soft=b042d000
[ 3.738173] Initializing CPU#1
[ 3.798912] Calibrating delay using timer specific routine.. 5986.12 BogoMIPS (lpj=2993061)
[ 3.798920] CPU: After generic identify, caps: bfebfbff 00000000 00000000 00000000 00004400 00000000 00000000 00000000
[ 3.798931] CPU: Trace cache: 12K uops, L1 D cache: 8K
[ 3.798934] CPU: L2 cache: 512K
[ 3.798936] CPU: Physical Processor ID: 0
[ 3.798938] CPU: After all inits, caps: bfebfbff 00000000 00000000 0000b080 00004400 00000000 00000000 00000000
[ 3.798946] Intel machine check architecture supported.
[ 3.798952] Intel machine check reporting enabled on CPU#1.
[ 3.798955] CPU1: Intel P4/Xeon Extended MCE MSRs (12) available
[ 3.798959] CPU1: Thermal monitoring enabled
[ 3.799161] CPU1: Intel(R) Pentium(R) 4 CPU 3.00GHz stepping 09
[ 3.799187] checking TSC synchronization [CPU#0 -> CPU#1]:
[ 3.819181] Measured 63588552840 cycles TSC warp between CPUs, turning off TSC clock.
[ 3.819184] Marking TSC unstable due to: check_tsc_sync_source failed.

If check_tsc_warp() is called after initial boot, and the TSC has in the
meantime been set (BIOS, user, silicon, elves) to a value lower than the
last stored/stale value, we blame the TSC. Reset to pristine condition
after every test.

Signed-off-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/kernel/tsc_sync.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

Index: linux-x86.q/arch/x86/kernel/tsc_sync.c
===================================================================
--- linux-x86.q.orig/arch/x86/kernel/tsc_sync.c
+++ linux-x86.q/arch/x86/kernel/tsc_sync.c
@@ -129,24 +129,24 @@ void __cpuinit check_tsc_sync_source(int
while (atomic_read(&stop_count) != cpus-1)
cpu_relax();

- /*
- * Reset it - just in case we boot another CPU later:
- */
- atomic_set(&start_count, 0);
-
if (nr_warps) {
printk("\n");
printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
" turning off TSC clock.\n", max_warp);
mark_tsc_unstable("check_tsc_sync_source failed");
- nr_warps = 0;
- max_warp = 0;
- last_tsc = 0;
} else {
printk(" passed.\n");
}

/*
+ * Reset it - just in case we boot another CPU later:
+ */
+ atomic_set(&start_count, 0);
+ nr_warps = 0;
+ max_warp = 0;
+ last_tsc = 0;
+
+ /*
* Let the target continue with the bootup:
*/
atomic_inc(&stop_count);
--
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