Messages in this thread | | | Subject | Re: [PATCH v8 1/5] x86: add simple udelay calibration | From | Dou Liyang <> | Date | Thu, 13 Jul 2017 09:39:38 +0800 |
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Hi, Lu
At 07/13/2017 09:17 AM, Lu Baolu wrote: > Hi, > > On 07/12/2017 04:02 PM, Dou Liyang wrote: >> Hi, Lu >> >> At 05/05/2017 08:50 PM, Boris Ostrovsky wrote: >>> On 05/05/2017 01:41 AM, Lu Baolu wrote: >>>> Hi, >>>> >>>> On 05/03/2017 06:38 AM, Boris Ostrovsky wrote: >>>>> On 03/21/2017 04:01 AM, Lu Baolu wrote: >>>>>> Add a simple udelay calibration in x86 architecture-specific >>>>>> boot-time initializations. This will get a workable estimate >>>>>> for loops_per_jiffy. Hence, udelay() could be used after this >>>>>> initialization. >>>>> This breaks Xen PV guests since at this point, and until >>>>> x86_init.paging.pagetable_init() which is when pvclock_vcpu_time_info is >>>>> mapped, they cannot access pvclock. >>>>> >>>>> Is it reasonable to do this before tsc_init() is called? (The failure >>>>> has nothing to do with tsc_init(), really --- it's just that it is >>>>> called late enough that Xen PV guests get properly initialized.) If it >>>>> is, would it be possible to move simple_udelay_calibration() after >>>>> x86_init.paging.pagetable_init()? >>>> This is currently only used for bare metal. How about by-pass it >>>> for Xen PV guests? >>> >>> It is fixed this for Xen PV guests now (in the sense that we don't crash >>> anymore) but my question is still whether this is not too early. Besides >>> tsc_init() (which might not be important here), at the time when >>> simple_udelay_calibration() is invoked we haven't yet called: >>> * kvmclock_init(), which sets calibration routines for KVM >>> * init_hypervisor_platform(), which sets calibration routines for vmware >>> and Xen HVM >>> * x86_init.paging.pagetable_init(), which sets calibration routines for >>> Xen PV >>> >> >> I guess these may have been missed. >> >> Do you have any comments about these? >> > > The patch will be available in 4.13-rc1.
Yes, I have seen it in the upstream.
Firstly, I also met this problem want to call udelay() earlier than *loops_per_jiffy* setup like you[1]. So I am very interesting in this patch. ;)
I am also confused about the questions which Boris asked:
whether do the CPU and TSC calibration too early just for using udelay()?
this design broke our interface of x86_paltform.calibrate_cpu/tsc.
And I also have a question below.
[...]
>>>>>> >>>>>> +static void __init simple_udelay_calibration(void) >>>>>> +{ >>>>>> + unsigned int tsc_khz, cpu_khz; >>>>>> + unsigned long lpj; >>>>>> + >>>>>> + if (!boot_cpu_has(X86_FEATURE_TSC)) >>>>>> + return;
if we don't have the TSC feature in booting CPU and it returns here, can we use udelay() correctly like before?
[1] https://lkml.org/lkml/2017/7/3/276
Thanks,
dou.
>> Thanks, >> >> dou. >> >>>>>> + >>>>>> + cpu_khz = x86_platform.calibrate_cpu(); >>>>>> + tsc_khz = x86_platform.calibrate_tsc(); >>>>>> + >>>>>> + tsc_khz = tsc_khz ? : cpu_khz; >>>>>> + if (!tsc_khz) >>>>>> + return; >>>>>> + >>>>>> + lpj = tsc_khz * 1000; >>>>>> + do_div(lpj, HZ); >>>>>> + loops_per_jiffy = lpj; >>>>>> +} >>>>>> + >>>>>> /* >>>>>> * Determine if we were loaded by an EFI loader. If so, then we have also been >>>>>> * passed the efi memmap, systab, etc., so we should use these data structures >>>>>> @@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p) >>>>>> */ >>>>>> x86_configure_nx(); >>>>>> >>>>>> + simple_udelay_calibration(); >>>>>> + >>>>>> parse_early_param(); >>>>>> >>>>>> #ifdef CONFIG_MEMORY_HOTPLUG >>> >>> >>> >>> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-usb" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > >
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