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Date: Tue, 24 Aug 2010 19:20:07 GMT
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To: freebsd-bugs@FreeBSD.org
From: Garrett Cooper <gcooper@FreeBSD.org>
Cc: 
Subject: Re: kern/145385: [cpu] Logical processor cannot be disabled for some
 SMT-enabled Intel procs
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The following reply was made to PR kern/145385; it has been noted by GNATS.

From: Garrett Cooper <gcooper@FreeBSD.org>
To: bug-followup@freebsd.org
Cc: jkim@freebsd.org, Attilio Rao <attilio@freebsd.org>, jeff@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@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