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Re: [WARNING] Intel Skylake/Kaby Lake processors: broken hyper-threading




Minor update on the issue:

The check command provided in the advisory to test for hyper-threading
doesn't work: it will always report hyper-theading as enabled.  A better
command is provided below.

Note: this also means the perl script will give some false-positives.
I apologise for the inconvenience.


On Sun, 25 Jun 2017, Henrique de Moraes Holschuh wrote:
> Once you know your processor model name, you can check the two lists
> below:
> 
>   * List of Intel processors code-named "Skylake":
>     http://ark.intel.com/products/codename/37572/Skylake
> 
>   * List of Intel processors code-named "Kaby Lake":
>     http://ark.intel.com/products/codename/82879/Kaby-Lake
> 
> Some of the processors in these two lists are not affected because they
> lack hyper-threading support.  Run the command below in a command line
> shell (e.g. xterm), and it will output a message if hyper-threading is
> supported/enabled:
> 
>   grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo && \
> 	echo "Hyper-threading is supported"

The above test (using "grep") does not work, and will always report that
hyper-threading is enabled.

Please use the "lscpu" utility from the util-linux package in a command
line shell (e.g.  xterm):

    lscpu

If the lscpu output reports: "Thread(s) per core: 2", that means
hyper-threading is enabled and supported.

If the lscpu output reports: "Thread(s) per core: 1", that means
hyper-threading either disabled or not supported.  In this case, the
specific defect mentioned in the advisory will not trigger.

-- 
  Henrique Holschuh