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Description of problem: Turing on HT on our IBM eServer xSeries 345: Type 8670 Model 31X machines makes the kernel loose about 1.5 seconds per each 10 seconds. Turing off HT in the BIOS makes everything happy again. Seems to have been introduced around kernel 2.6.20-1.2952.fc6, continues to exist in 2.6.20-1.2962.fc6. Version-Release number of selected component (if applicable): 2.6.20-1.2952.fc6, 2.6.20-1.2962.fc6 How reproducible: Definitely reproducable on our two HT-capable boxes -- both IBM eseries x345 machines. Our other non-HT intel / PPC boxes running same kernels don't exhibit time issues. Steps to Reproduce: 1. Take BM eseries x345 (or possibly other era older xeon HT machine) 2. Enable HT 3. Boot 4. Watch clock loose time, regardless of ntpd. Then disable HT, and all's happy. Actual results: ntpd can't keep clock adjusted, gettimeofday gets worse and worse off. Expected results: kernel keeps proper time just like it did before with HT enabled, or like it does with HT disabled. Additional info: See attachment for time drift measurements with ntpd off, varying HT enabled versus disabled.
Created attachment 159325 [details] time drift measurements with ntpd off, varying HT enabled versus disabled.
Oh yeah -- these machines are SMP -- 2 2.4Ghz Xeons. So with HT enabled, kernel shows 'em as having 4 CPUs. Here's what /proc/cpuinfo has to say about 'em with HT off, if that helps in finding a machine to test against: [root@build-db02 ~]# cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 2 model name : Intel(R) Xeon(TM) CPU 2.40GHz stepping : 7 cpu MHz : 2602.628 cache size : 512 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 2 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr bogomips : 7186.29 clflush size : 64 processor : 1 vendor_id : GenuineIntel cpu family : 15 model : 2 model name : Intel(R) Xeon(TM) CPU 2.40GHz stepping : 7 cpu MHz : 2602.628 cache size : 512 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 2 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr bogomips : 7189.95 clflush size : 64
Grr. Spoke too soon. Disabling HT doesn't help at all -- time still drifts uncontrollably. Will close bug out and gather better data and then resubmit.