From owner-freebsd-bugs@FreeBSD.ORG Tue Aug 24 21:10:10 2010 Return-Path: Delivered-To: freebsd-bugs@hub.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9A96C1065694 for ; Tue, 24 Aug 2010 21:10:10 +0000 (UTC) (envelope-from gnats@FreeBSD.org) Received: from freefall.freebsd.org (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx1.freebsd.org (Postfix) with ESMTP id 896408FC12 for ; Tue, 24 Aug 2010 21:10:10 +0000 (UTC) Received: from freefall.freebsd.org (localhost [127.0.0.1]) by freefall.freebsd.org (8.14.4/8.14.4) with ESMTP id o7OLAAhK033619 for ; Tue, 24 Aug 2010 21:10:10 GMT (envelope-from gnats@freefall.freebsd.org) Received: (from gnats@localhost) by freefall.freebsd.org (8.14.4/8.14.4/Submit) id o7OLAA5t033618; Tue, 24 Aug 2010 21:10:10 GMT (envelope-from gnats) Date: Tue, 24 Aug 2010 21:10:10 GMT Message-Id: <201008242110.o7OLAA5t033618@freefall.freebsd.org> To: freebsd-bugs@FreeBSD.org From: Jeff Roberson Cc: Subject: Re: kern/145385: [cpu] Logical processor cannot be disabled for some SMT-enabled Intel procs X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Jeff Roberson List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Aug 2010 21:10:10 -0000 The following reply was made to PR kern/145385; it has been noted by GNATS. From: Jeff Roberson To: Garrett Cooper Cc: bug-followup@freebsd.org, jkim@freebsd.org, Attilio Rao , jeff@freebsd.org Subject: Re: kern/145385: [cpu] Logical processor cannot be disabled for some SMT-enabled Intel procs Date: Tue, 24 Aug 2010 11:03:40 -1000 (HST) This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --2547152148-2115359276-1282683824=:1407 Content-Type: TEXT/PLAIN; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8BIT On Tue, 24 Aug 2010, Garrett Cooper wrote: > On Tue, Aug 24, 2010 at 12:22 PM, Jeff Roberson wrote: >> On Tue, 24 Aug 2010, Garrett Cooper wrote: >> >>> On Mon, Aug 23, 2010 at 6:33 AM, John Baldwin wrote: >>>> >>>> On Sunday, August 22, 2010 4:17:37 am Garrett Cooper wrote: >>>>> >>>>>       The following trivial patch fixes the issue on my W3520 processor; >>>>> 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 >>>> multi-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=1 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? >>> >> >> hlt_logical_cpus should be rewritten to use cpusets to change the default >> system set rather than specifically halting those cpus.  There are a number >> of loops in the kernel that iterate over all cpus and attempt to bind and >> perform some task.  I think there are a number of other reasons to prefer a >> less aggressive approach to avoiding the logical cpus as well. Simply >> preventing user thread schedule will achieve the intent of the sysctl in any >> event. > > Ok... in that event then the bug is ok, but maybe I should add > some code to the patch to warn the user about functional issues > associated with halting logical CPUs? I don't think the bug is ok. We probably shouldn't have sysctls which readily break the kernel. As I said we should instead have the sysctl backend to cpuset. It shouldn't take more than an hour to code and test. Thanks, Jeff > Thanks! > -Garrett > --2547152148-2115359276-1282683824=:1407--