linux-kernel - Possible SNB throttling erratum in need of workaround?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 18 Dec 2013 18:02:34 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Possible SNB throttling erratum in need of workaround?

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/