Messages in this thread | | | From | Jianyong Wu <> | Subject | RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 | Date | Mon, 7 Sep 2020 08:51:23 +0000 |
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Hi Marc,
> -----Original Message----- > From: Marc Zyngier <maz@kernel.org> > Sent: Saturday, September 5, 2020 7:33 PM > To: Jianyong Wu <Jianyong.Wu@arm.com> > Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org; > tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com; > richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>; > will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Steven Price > <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm- > kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu; > kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He > <Justin.He@arm.com>; nd <nd@arm.com> > Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 > > On Fri, 04 Sep 2020 10:27:42 +0100, > Jianyong Wu <jianyong.wu@arm.com> wrote: > > > > Currently, there is no mechanism to keep time sync between guest and > > host in 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 > > envirenment, we ask for higher time precision. > > > > kvm ptp clock, which choose the host clock source as a reference clock > > to sync time between guest and host, has been adopted by x86 which > > makes the time sync order from milliseconds to nanoseconds. > > > > This patch enables kvm ptp clock for arm64 and improve clock sync > > precison significantly. > > > > Test result comparisons between with kvm ptp clock and without it in > > arm64 are as follows. This test derived from the result of command > > 'chronyc sources'. we should take more care of the last sample column > > which shows the offset between the local clock and the source at the last > measurement. > > > > no kvm ptp in guest: > > MS Name/IP address Stratum Poll Reach LastRx Last sample > > > ========================================================== > ============== > > ^* dns1.synet.edu.cn 2 6 377 13 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 21 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 29 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 37 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 45 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 53 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 61 +1040us[+1581us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 4 -130us[ +796us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 12 -130us[ +796us] +/- 21ms > > ^* dns1.synet.edu.cn 2 6 377 20 -130us[ +796us] +/- 21ms > > > > in host: > > MS Name/IP address Stratum Poll Reach LastRx Last sample > > > ========================================================== > ============== > > ^* 120.25.115.20 2 7 377 72 -470us[ -603us] +/- 18ms > > ^* 120.25.115.20 2 7 377 92 -470us[ -603us] +/- 18ms > > ^* 120.25.115.20 2 7 377 112 -470us[ -603us] +/- 18ms > > ^* 120.25.115.20 2 7 377 2 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 22 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 43 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 63 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 83 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 103 +872ns[-6808ns] +/- 17ms > > ^* 120.25.115.20 2 7 377 123 +872ns[-6808ns] +/- 17ms > > > > The dns1.synet.edu.cn is the network reference clock for guest and > > 120.25.115.20 is the network reference clock for host. we can't get > > the clock error between guest and host directly, but a roughly > > estimated value will be in order of hundreds of us to ms. > > > > with kvm ptp in guest: > > chrony has been disabled in host to remove the disturb by network clock. > > > > MS Name/IP address Stratum Poll Reach LastRx Last sample > > > ========================================================== > ============== > > * PHC0 0 3 377 8 -7ns[ +1ns] +/- 3ns > > * PHC0 0 3 377 8 +1ns[ +16ns] +/- 3ns > > * PHC0 0 3 377 6 -4ns[ -0ns] +/- 6ns > > * PHC0 0 3 377 6 -8ns[ -12ns] +/- 5ns > > * PHC0 0 3 377 5 +2ns[ +4ns] +/- 4ns > > * PHC0 0 3 377 13 +2ns[ +4ns] +/- 4ns > > * PHC0 0 3 377 12 -4ns[ -6ns] +/- 4ns > > * PHC0 0 3 377 11 -8ns[ -11ns] +/- 6ns > > * PHC0 0 3 377 10 -14ns[ -20ns] +/- 4ns > > * PHC0 0 3 377 8 +4ns[ +5ns] +/- 4ns > > > > The PHC0 is the ptp clock which choose the host clock as its source > > clock. So we can see that the clock difference between host and guest > > is in order of ns. > > > > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> > > --- > > drivers/clocksource/arm_arch_timer.c | 24 +++++++++++++ > > drivers/ptp/Kconfig | 2 +- > > drivers/ptp/ptp_kvm_arm64.c | 53 > ++++++++++++++++++++++++++++ > > 3 files changed, 78 insertions(+), 1 deletion(-) create mode 100644 > > drivers/ptp/ptp_kvm_arm64.c > > And I missed that one earlier: > > > diff --git a/drivers/clocksource/arm_arch_timer.c > > b/drivers/clocksource/arm_arch_timer.c > > index d55acffb0b90..aaf286e90092 100644 > > --- a/drivers/clocksource/arm_arch_timer.c > > +++ b/drivers/clocksource/arm_arch_timer.c > > @@ -1650,3 +1650,27 @@ static int __init arch_timer_acpi_init(struct > > acpi_table_header *table) } TIMER_ACPI_DECLARE(arch_timer, > > ACPI_SIG_GTDT, arch_timer_acpi_init); #endif > > + > > +#if IS_ENABLED(CONFIG_PTP_1588_CLOCK_KVM) > > +#include <linux/arm-smccc.h> > > No conditional includes, please. > Ok.
> > +int kvm_arch_ptp_get_crosststamp(unsigned long *cycle, struct > timespec64 *ts, > > + struct clocksource **cs) > > +{ > > + struct arm_smccc_res hvc_res; > > + ktime_t ktime; > > + > > + /* Currently, linux guest will always use the virtual counter */ > > + > arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU > NC_ID, > > + ARM_PTP_VIRT_COUNTER, &hvc_res); > > You don't need to assume anything. This driver already provides you with the > information you need to tell the hypervisor which counter to > use: > > if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) > ptp_counter = ARM_PTP_VIRT_COUNTER; > else > ptp_counter = ARM_PTP_PHYS_COUNTER; > arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU > NC_ID, > ptp_counter, &hvc_res); > > At least, this is vaguely future proof. > > The hypervisor will still have to discriminate between a call between a call > from vEL1 or vEL2 to decide whether to subtract the offset from the counter > value, but that's out of scope for now.
Very kind of you!
Thanks Jianyong > > M. > > -- > Without deviation from the norm, progress is not possible.
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