Date: Wed, 5 May 2010 16:26:27 -0700 (PDT) From: Hubert Tournier <hubert@frbsd.org> To: freebsd-smp@freebsd.org Subject: Re: Disabling HyperThreading? Message-ID: <28467645.post@talk.nabble.com> In-Reply-To: <p2yab581e311005050841ob19af115gca86fe06278796a@mail.gmail.com> References: <28357071.post@talk.nabble.com> <4BD4727F.4060700@googlemail.com> <28359495.post@talk.nabble.com> <4BD563F7.4010203@googlemail.com> <201004260948.12730.jhb@freebsd.org> <p2yab581e311005050841ob19af115gca86fe06278796a@mail.gmail.com>
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Hello, Jack L.-3 wrote: > > sysctl machdep.hyperthreading_allowed=0 will disable it. > Thank you for this lead. It gives the following result on my system: sysctl: unknown oid 'machdep.hyperthreading_allowed' Searching a little bit, i found 2 references to this OID in the kernel source code: /usr/src/sys/amd64/amd64/mp_machdep.c /usr/src/sys/i386/i386/mp_machdep.c Maybe it's missing because (as i read in these files): SCHED_ULE doesn't allow enabling/disabling HT cores at run-time. I'm not sure i could use the OID in /boot/loader.conf however? I also see in the source code that the default is to enable HT cores: static int hyperthreading_allowed = 1; So i will test a custom kernel with this disabled. For reference, here is the CPU i use: CPU: Intel(R) Xeon(R) CPU X5650 @ 2.67GHz (2666.65-MHz K8-class CPU) Origin = "GenuineIntel" Id = 0x206c2 Stepping = 2 Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE> Features2=0x9ee3fd<SSE3,DTES64,MON,DS_CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,<b17>,DCA,SSE4.1,SSE4.2,POPCNT> AMD Features=0x2c100800<SYSCALL,NX,Page1GB,RDTSCP,LM> AMD Features2=0x1<LAHF> TSC: P-state invariant FreeBSD/SMP: Multiprocessor System Detected: 24 CPUs FreeBSD/SMP: 2 package(s) x 6 core(s) x 2 SMT threads Best regards, Hubert -- View this message in context: http://old.nabble.com/Disabling-HyperThreading--tp28357071p28467645.html Sent from the freebsd-smp mailing list archive at Nabble.com.
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