kern/145385: [cpu] Logical processor cannot be disabled for some
SMT-enabled Intel procs
Garrett Cooper
gcooper at FreeBSD.org
Tue Aug 24 19:20:08 UTC 2010
The following reply was made to PR kern/145385; it has been noted by GNATS.
From: Garrett Cooper <gcooper at FreeBSD.org>
To: bug-followup at freebsd.org
Cc: jkim at freebsd.org, Attilio Rao <attilio at freebsd.org>, jeff at FreeBSD.org
Subject: Re: kern/145385: [cpu] Logical processor cannot be disabled for some
SMT-enabled Intel procs
Date: Tue, 24 Aug 2010 12:15:41 -0700
On Mon, Aug 23, 2010 at 6:33 AM, John Baldwin <jhb at freebsd.org> wrote:
> On Sunday, August 22, 2010 4:17:37 am Garrett Cooper wrote:
>> =A0 =A0 =A0 The following trivial patch fixes the issue on my W3520 proc=
essor; AFAICS
> it's what should be done after reading several of the specs because the
> logical count that's tracked with ebx is exactly what is needed for
> logical_cpus (it's an absolute quantity). I need to verify it with a mult=
i-cpu
> topology at work (the two r710s I was testing with E-series Xeons on aren=
't
> available remotely right now).
>> Thanks!
>> -Garrett
>
> Jung-uk Kim and Attilio Rao have both been looking at this code recently =
and
> are in a better position to review the patch in the PR.
(Moving jhb@ to BCC, adding jeff@ for possible input on ULE)
The patch works as expected (it now properly detects the SMIT CPUs as
logical CPUs), but setting machdep.hlt_logical_cpus=3D1 causes other
problems with scheduling tasks because certain kernel threads get
stuck at boot when netbooting (in particular I've seen problems with
usbhub* and a few others bits), so in order for
machdep.hlt_logical_cpus to be fixed on SMT processors, it might
require some changes to the ULE scheduler to shuffle around the
threads to available cores/processors?
Thanks!
-Garrett
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