Date: Wed, 9 Sep 2009 13:24:53 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-stable@freebsd.org Cc: Luigi Rizzo <rizzo@iet.unipi.it> Subject: Re: incorrect usleep/select delays with HZ > 2500 Message-ID: <200909091324.53668.jhb@freebsd.org> In-Reply-To: <20090908210100.GA72735@onelab2.iet.unipi.it> References: <20090906155154.GA8283@onelab2.iet.unipi.it> <200909081308.23345.jhb@freebsd.org> <20090908210100.GA72735@onelab2.iet.unipi.it>
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On Tuesday 08 September 2009 5:01:00 pm Luigi Rizzo wrote: > On Tue, Sep 08, 2009 at 01:08:23PM -0400, John Baldwin wrote: > > On Sunday 06 September 2009 11:51:54 am Luigi Rizzo wrote: > > > [Note 3] the TSC frequency is computed reading the tsc around a > > > call to DELAY(1000000) and assuming that the i8254 runs > > > at the nominal rate, 1.193182 MHz. > > > From tests I have made, the measurement in init_TSC() returns > > > a large error when HZ is large, whereas repeating the measurement > > > at a later time returns a much more reliable value. > > > As an example, see the following: > > > > > > Sep 6 14:21:59 lr kernel: TSC clock: at init_TSC 2323045616 Hz > > > Sep 6 14:21:59 lr kernel: > > Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT> > > > Sep 6 14:21:59 lr kernel: AMD > > Features=0xea500800<SYSCALL,NX,MMX+,FFXSR,RDTSCP,LM,3DNow!+,3DNow!> > > > Sep 6 14:21:59 lr kernel: TSC: P-state invariant > > > Sep 6 14:21:59 lr kernel: TSC clock: at cpu_startup_end 2323056910 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at acpi_timer_probe 2311254060 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at acpi_timer_probe_2 2311191310 > > Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at pn_probe_start 2300822648 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at pn_attach_start 2300830946 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at pn_probe_start 2300840133 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at pn_attach_start 2300835253 Hz > > > Sep 6 14:21:59 lr kernel: TSC clock: at lapic_setup_clock 2300868376 Hz > > > > > > The latter values are close to what is reported when HZ=1000. > > > > Try disabling legacy USB support in the BIOS to see if an SMI# is firing > > during the DELAY() causing the TSC freq to be too high. I have seen the USB > > legacy support cause this in other machines. > > Thanks, will try tomorrow. > Would this explain the measurement becomes better as we get > further into the initialization, and why high HZ values affect > the measurement ? It would explain why it gets better later since the uhci(4), ohci(4) and ehci(4) drivers disable the SMI# interrupts while attaching to the controllers. -- John Baldwin
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