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SubjectRE: [RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64
Date
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Tuesday, January 7, 2020 5:29 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>; Kaly Xin
> <Kaly.Xin@arm.com>; Justin He <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64
>
> On 2019-12-10 03:40, Jianyong Wu wrote:
> > Currently in arm64 virtualization environment, there is no mechanism
> > to keep time sync between guest and host. 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 some scenarios ask for higher time
> > precision, like in cloud envirenment, we want all the VMs running in
> > the host aquire the same level accuracy from host clock.
> >
> > Use of kvm ptp clock, which choose the host clock source clock as a
> > reference clock to sync time clock between guest and host has been
> > adopted by x86 which makes the time sync order from milliseconds to
> > nanoseconds.
> >
> > This patch enable kvm ptp on arm64 and we get the similar clock drift
> > as found with x86 with kvm ptp.
> >
> > Test result comparison between with kvm ptp and without it in arm64
> > are as follows. This test derived from the result of command 'chronyc
> > sources'. we should take more cure 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 be sure to say that the clock error between host and
> > guest is in order of ns.
> >
> > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> > ---
> > drivers/clocksource/arm_arch_timer.c | 22 ++++++++++++
> > drivers/ptp/Kconfig | 2 +-
> > drivers/ptp/ptp_kvm_arm64.c | 53
> ++++++++++++++++++++++++++++
> > 3 files changed, 76 insertions(+), 1 deletion(-) create mode 100644
> > drivers/ptp/ptp_kvm_arm64.c
> >
> > diff --git a/drivers/clocksource/arm_arch_timer.c
> > b/drivers/clocksource/arm_arch_timer.c
> > index 277846decd33..72260b66f02e 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -1636,3 +1636,25 @@ 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>
> > +int kvm_arch_ptp_get_crosststamp(unsigned long *cycle, struct
> > timespec64 *ts,
> > + struct clocksource **cs)
> > +{
> > + struct arm_smccc_res hvc_res;
> > + ktime_t ktime_overall;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID, &hvc_res);
> > + if ((long)(hvc_res.a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + ktime_overall = hvc_res.a0 << 32 | hvc_res.a1;
> > + *ts = ktime_to_timespec64(ktime_overall);
> > + *cycle = hvc_res.a2 << 32 | hvc_res.a3;
>
> So why isn't that just a read of the virtual counter, given that what you do in
> the hypervisor seems to be "cntpct - cntvoff"?
>
> What am I missing here?
>
We need get clock time and counter cycle at the same time, so we can't just read virtual counter
at guest and must get it from host.

> > + *cs = &clocksource_counter;
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
> > +#endif
> > diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig index
> > 9b8fee5178e8..3c31ff8eb05f 100644
> > --- a/drivers/ptp/Kconfig
> > +++ b/drivers/ptp/Kconfig
> > @@ -110,7 +110,7 @@ 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 || ARM64 && ARM_ARCH_TIMER
> > default y
> > help
> > This driver adds support for using kvm infrastructure as a PTP
> > diff --git a/drivers/ptp/ptp_kvm_arm64.c b/drivers/ptp/ptp_kvm_arm64.c
> > new file mode 100644 index 000000000000..f3f957117865
> > --- /dev/null
> > +++ b/drivers/ptp/ptp_kvm_arm64.c
> > @@ -0,0 +1,53 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Virtual PTP 1588 clock for use with KVM guests
> > + * Copyright (C) 2019 ARM Ltd.
> > + * All Rights Reserved
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/err.h>
> > +#include <asm/hypervisor.h>
> > +#include <linux/module.h>
> > +#include <linux/psci.h>
> > +#include <linux/arm-smccc.h>
> > +#include <linux/timecounter.h>
> > +#include <linux/sched/clock.h>
> > +#include <asm/arch_timer.h>
> > +
> > +int kvm_arch_ptp_init(void)
> > +{
> > + struct arm_smccc_res hvc_res;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + &hvc_res);
> > + if ((long)(hvc_res.a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + return 0;
> > +}
> > +
> > +int kvm_arch_ptp_get_clock_generic(struct timespec64 *ts,
> > + struct arm_smccc_res *hvc_res) {
> > + ktime_t ktime_overall;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + hvc_res);
> > + if ((long)(hvc_res->a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + ktime_overall = hvc_res->a0 << 32 | hvc_res->a1;
> > + *ts = ktime_to_timespec64(ktime_overall);
> > +
> > + return 0;
> > +}
> > +
> > +int kvm_arch_ptp_get_clock(struct timespec64 *ts) {
> > + struct arm_smccc_res hvc_res;
> > +
> > + kvm_arch_ptp_get_clock_generic(ts, &hvc_res);
> > +
> > + return 0;
> > +}
>
> I also wonder why this is all arm64 specific, while everything should also work
> just fine on 32bit.
>
ptp_kvm is a feature for cloud computing to keep time consistency from container to container and to host on server,
So we focus it on arm64. Also I have never tested it on arm32 machine ( we lack of arm32 machine)
Do you think it's necessary to enable ptp_kvm on arm32? If so, I can do that.

Thanks
Jianyong

> M.
> --
> Jazz is not dead. It just smells funny...

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