Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 7 Jan 2014 14:02:49 -0800 | Subject | Re: Possible SNB throttling erratum in need of workaround? |
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[cc: some more people]
On Wed, Dec 18, 2013 at 6:02 PM, Andy Lutomirski <luto@amacapital.net> wrote: > I have a box running 3.9.4. For a few hundred ms, all packages and > cores* exceeded their power limits, and then they all came back to > normal. > > Since then, turbo boost went away. > > The first thing I tried was writing 0 to msr 0x19C to clear the > throttling "log" bit. The bit was clear, but still no turbo. (I only > did this on one package to avoid destroying information.) > > I have the performance governor set, so there are never any > software-initiated performance transitions. As an experiment, I > switched core 0 to powersave (aka very low frequency) and then back to > performance. The entire package's turbo came back. I did the same > thing to the cores on package 1 (all of them, sorry), and that > package's turbo boost came back. > > Does the kernel need to reprogram CPU frequencies after thermal/power > throttling conditions clear? > > My CPUs are: > > processor : 31 > vendor_id : GenuineIntel > cpu family : 6 > model : 45 > model name : Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz > stepping : 7 > microcode : 0x710 > > > * Slight lie here. CPU18 exceeded core limit but not power limit.
I got another power-limit-exceeded warning, but this one didn't kill Turbo.
This problem might be more widespread than people would notice, because the log line was removed by:
commit c81147483e525e4a471d581877d7d634591246e1 Author: Fenghua Yu <fenghua.yu@intel.com> Date: Tue May 21 15:35:16 2013 -0400
x86 thermal: Delete power-limit-notification console messages
and if the only symptom is that, under certain workloads, turbo goes away until the system is rebooted or cpufreq is manually twiddled, people might not notice.
--Andy
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