> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: Tuesday, August 27, 2013 12:26 AM > To: KY Srinivasan > Cc: olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; x86@xxxxxxxxxx; > devel@xxxxxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; > jasowang@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; hpa@xxxxxxxxx > Subject: Re: [PATCH 1/1] X86: Hyper-V: Get the local APIC timer frequency from > the hypervisor > > >>> On 27.08.13 at 01:42, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> wrote: > > Hyper-V supports a mechanism for retrieving the local API frequency. > > "APIC"? > > > @@ -27,6 +27,13 @@ > > #define HV_X64_MSR_VP_RUNTIME_AVAILABLE (1 << 0) > > /* Partition Reference Counter (HV_X64_MSR_TIME_REF_COUNT) available*/ > > #define HV_X64_MSR_TIME_REF_COUNT_AVAILABLE (1 << 1) > > + > > +/* Local APIC timer frequency MSR (HV_X64_MSR_APIC_FREQUENCY) is > available */ > > +#define HV_X64_MSR_APIC_FREQUENCY_AVAILABLE (1 << 11) > > + > > +/* TSC frequency MSR (HV_X64_MSR_TSC_FREQUENCY) is available */ > > +#define HV_X64_MSR_TSC_FREQUENCY_AVAILABLE (1 << 11) > > Are these two really the same bit? If so, why two different names? > > > @@ -136,6 +143,12 @@ > > /* MSR used to read the per-partition time reference counter */ > > #define HV_X64_MSR_TIME_REF_COUNT 0x40000020 > > > > +/* MSR used to retrive the TSC frequency */ > > +#define HV_X64_MSR_TSC_FREQUENCY 0x40000022 > > + > > +/* MSR used to retrive the local APIC timer frequency */ > > +#define HV_X64_MSR_APIC_FREQUENCY 0x40000023 > > "retrieve" (twice)? > > > @@ -76,6 +77,22 @@ static void __init ms_hyperv_init_platform(void) > > printk(KERN_INFO "HyperV: features 0x%x, hints 0x%x\n", > > ms_hyperv.features, ms_hyperv.hints); > > > > + if (ms_hyperv.features & HV_X64_MSR_APIC_FREQUENCY_AVAILABLE) { > > + /* > > + * There is no need to calibrate APIC timer frequency; > > + * nor is there a need to calibrate timer. > > + */ > > + legacy_pic = &null_legacy_pic; > > This clearly disables more than just the calibration, so the comment > may be misleading to future readers. > > > + > > + /* > > + * Get the APIC frequency. > > + */ > > + rdmsrl(HV_X64_MSR_APIC_FREQUENCY, > lapic_timer_frequency); > > + lapic_timer_frequency /= HZ; > > Is this safe? I.e. are the high 32 bits of the MSR guaranteed to > be zero, now and forever? > > > + printk(KERN_INFO "HyperV: LAPIC Timer Frequency: 0x%x\n", > > + lapic_timer_frequency); > > As a minor note, I generally recommend using %#x as being one > byte shorter than the spelled out 0x%x. > > Jan Thanks Jan. I will fix the issues you have pointed out and resubmit the patch. Regards, K. Y _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
