linux-kernel - regression in TSC unstable?

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Date:	Fri, 8 May 2009 00:14:44 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Len Brown <len.brown@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>
Subject: regression in TSC unstable?


The ring-buffer-benchmark module creates a producer and consumer and loops 
on do_gettimeofday until it hits about 10 seconds. Then it calculates the 
number of events recorded / time running.

After Ingo merged Linus's latest my tests when from 330ns per entry to 
880ns. After bisecting it I came down to this change:

   commit a71e4917dc0ebbcb5a0ecb7ca3486643c1c9a6e2
   Author: Len Brown <len.brown@...el.com>
   Date:   Tue Apr 21 00:50:11 2009 -0400

    ACPI: idle: mark_tsc_unstable() at init-time, not run-time


I've never had a problem with the TSC with this box before. It passes the 
synchronization phase, and until this commit, the TSC never was marked as 
unstable.

Should it now be unstable? Or is this a false positive?

# cat /proc/cpuinfo 
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 15
model		: 4
model name	: Intel(R) Xeon(TM) CPU 2.80GHz
stepping	: 1
cpu MHz		: 2793.272
cache size	: 1024 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 5
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx 
lm constant_tsc pebs bts pni dtes64 monitor ds_cpl cid cx16 xtpr
bogomips	: 5586.54
clflush size	: 64
cache_alignment	: 128
address sizes	: 36 bits physical, 48 bits virtual
power management:

Anything else I might need to know?

-- Steve

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