The following reply was made to PR kern/145385; it has been noted by GNATS.
From: Garrett Cooper <[email protected]> To: Jeff Roberson <[email protected]> Cc: [email protected], [email protected], Attilio Rao <[email protected]>, [email protected] Subject: Re: kern/145385: [cpu] Logical processor cannot be disabled for some SMT-enabled Intel procs Date: Tue, 24 Aug 2010 14:00:19 -0700 On Tue, Aug 24, 2010 at 12:22 PM, Jeff Roberson <[email protected]> w= rote: > On Tue, 24 Aug 2010, Garrett Cooper wrote: > >> On Mon, Aug 23, 2010 at 6:33 AM, John Baldwin <[email protected]> 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 pr= ocessor; >>>> 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 recentl= y >>> 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? >> > > hlt_logical_cpus should be rewritten to use cpusets to change the default > system set rather than specifically halting those cpus. =A0There are a nu= mber > of loops in the kernel that iterate over all cpus and attempt to bind and > perform some task. =A0I think there are a number of other reasons to pref= er 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? Thanks! -Garrett _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-bugs To unsubscribe, send any mail to "[email protected]"
