Hi Marc, On Tue, May 11, 2021 at 11:13 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > On 2021-05-11 10:07, Geert Uytterhoeven wrote: > > On Tue, Mar 30, 2021 at 4:56 PM Marc Zyngier <maz@xxxxxxxxxx> wrote: > >> From: Jianyong Wu <jianyong.wu@xxxxxxx> > >> > >> Currently, there is no mechanism to keep time sync between guest and > >> host > >> in arm/arm64 virtualization environment. Time in guest will drift > >> compared > >> with host after boot up as they may both use third party time sources > >> to correct their time respectively. The time deviation will be in > >> order > >> of milliseconds. But in some scenarios,like in cloud environment, we > >> ask > >> for higher time precision. > >> > >> kvm ptp clock, which chooses the host clock source as a reference > >> clock to sync time between guest and host, has been adopted by x86 > >> which takes the time sync order from milliseconds to nanoseconds. > >> > >> This patch enables kvm ptp clock for arm/arm64 and improves clock sync > >> precision > >> significantly. > > > >> --- a/drivers/ptp/Kconfig > >> +++ b/drivers/ptp/Kconfig > >> @@ -108,7 +108,7 @@ config PTP_1588_CLOCK_PCH > >> config PTP_1588_CLOCK_KVM > >> tristate "KVM virtual PTP clock" > >> depends on PTP_1588_CLOCK > >> - depends on KVM_GUEST && X86 > >> + depends on (KVM_GUEST && X86) || (HAVE_ARM_SMCCC_DISCOVERY && > >> ARM_ARCH_TIMER) > > > > Why does this not depend on KVM_GUEST on ARM? > > I.e. shouldn't the dependency be: > > > > KVM_GUEST && (X86 || (HAVE_ARM_SMCCC_DISCOVERY && ARM_ARCH_TIMER)) > > > > ? > > arm/arm64 do not select KVM_GUEST. Any kernel can be used for a guest, > and KVM/arm64 doesn't know about this configuration symbol. OK. Does PTP_1588_CLOCK_KVM need to default to yes? Perhaps only on X86, to maintain the status quo? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm