linux-kernel - TSC unstable due to TSC halts in idle?

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Date:	Fri, 14 May 2010 22:13:57 +0200 (CEST)
From:	Jesper Dangaard Brouer <hawk@...u.dk>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	Shaohua Li <shaohua.li@...el.com>, hawk@...x.dk
Subject: TSC unstable due to TSC halts in idle?


Hi Thomas,

I want to know, if its safe to enable the TSC clocksource, when the
kernel reports:
  "Marking TSC unstable due to TSC halts in idle"

The system selects HPET (in current_clocksource), but I can still see
TSC as an available clocksource (in
/sys/devices/system/clocksource/clocksource0/available_clocksource).

Is it safe to enable TSC manually (by changing current_clocksource)?
(my workload is 10Git/s routing, cannot survive with a slow clock)


Any trick to avoid this? (e.g. kernel config setting, or a /sys/ setting
which changes the minimum P-state?)


The system is a new HP370-G6 server, with two Xeon X5550 CPUs.  Its
(currently) running a Debian compiled kernel 2.6.26-2-amd64.

Kernel log:
  checking TSC synchronization [CPU#0 -> CPU#1]: passed.
  checking TSC synchronization [CPU#0 -> CPU#2]: passed.
  ...
  checking TSC synchronization [CPU#0 -> CPU#14]: passed.
  checking TSC synchronization [CPU#0 -> CPU#15]: passed.
  Marking TSC unstable due to TSC halts in idle


Cheers,
   Jesper Brouer

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