RE: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

Jianyong Wu
2020-11-24T05:38:06Z

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, November 23, 2020 6:49 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>; Andre
> Przywara <Andre.Przywara@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 v15 7/9] ptp: arm/arm64: Enable ptp_kvm for
> arm/arm64
>
> On 2020-11-11 06:22, Jianyong Wu wrote:
> > 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
> > envirenment, we ask
>
> environment
>
OK

> > 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
> > precison
>
> precision
>
OK

> > significantly.
> >
> > Test result comparisons between with kvm ptp clock and without it in
> > arm/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 | 28 ++++++++++++++++++
> > drivers/ptp/Kconfig | 2 +-
> > drivers/ptp/Makefile | 1 +
> > drivers/ptp/ptp_kvm_arm.c | 44
> ++++++++++++++++++++++++++++
> > 4 files changed, 74 insertions(+), 1 deletion(-) create mode 100644
> > drivers/ptp/ptp_kvm_arm.c
> >
> > diff --git a/drivers/clocksource/arm_arch_timer.c
> > b/drivers/clocksource/arm_arch_timer.c
> > index d55acffb0b90..b33c5a663d30 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -25,6 +25,7 @@
> > #include <linux/sched/clock.h>
> > #include <linux/sched_clock.h>
> > #include <linux/acpi.h>
> > +#include <linux/arm-smccc.h>
> >
> > #include <asm/arch_timer.h>
> > #include <asm/virt.h>
> > @@ -1650,3 +1651,30 @@ 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
> > +
> > +int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *ts,
> > + struct clocksource **cs)
> > +{
> > + struct arm_smccc_res hvc_res;
> > + ktime_t ktime;
> > + u32 ptp_counter;
> > +
> > + if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
> > + ptp_counter = ARM_PTP_VIRT_COUNTER;
> > + else
> > + ptp_counter = ARM_PTP_PHY_COUNTER;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + ptp_counter, &hvc_res);
> > +
> > + if ((int)(hvc_res.a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + ktime = (u64)hvc_res.a0 << 32 | hvc_res.a1;
> > + *ts = ktime_to_timespec64(ktime);
> > + *cycle = (u64)hvc_res.a2 << 32 | hvc_res.a3;
>
> Endianness.
>
> > + *cs = &clocksource_counter;
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
> > diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig index
> > 942f72d8151d..677c7f696b70 100644
> > --- a/drivers/ptp/Kconfig
> > +++ b/drivers/ptp/Kconfig
> > @@ -106,7 +106,7 @@ 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)
> > default y
> > help
> > This driver adds support for using kvm infrastructure as a PTP
> > diff --git a/drivers/ptp/Makefile b/drivers/ptp/Makefile index
> > 699a4e4d19c2..9fa5ede44b2b 100644
> > --- a/drivers/ptp/Makefile
> > +++ b/drivers/ptp/Makefile
> > @@ -5,6 +5,7 @@
> >
> > ptp-y := ptp_clock.o ptp_chardev.o
> ptp_sysfs.o
> > ptp_kvm-$(CONFIG_X86) := ptp_kvm_x86.o
> ptp_kvm_common.o
> > +ptp_kvm-$(CONFIG_HAVE_ARM_SMCCC) := ptp_kvm_arm.o
> ptp_kvm_common.o
> > obj-$(CONFIG_PTP_1588_CLOCK) += ptp.o
> > obj-$(CONFIG_PTP_1588_CLOCK_DTE) += ptp_dte.o
> > obj-$(CONFIG_PTP_1588_CLOCK_INES) += ptp_ines.o
> > diff --git a/drivers/ptp/ptp_kvm_arm.c b/drivers/ptp/ptp_kvm_arm.c new
> > file mode 100644 index 000000000000..2212827c0384
> > --- /dev/null
> > +++ b/drivers/ptp/ptp_kvm_arm.c
> > @@ -0,0 +1,44 @@
> > +// 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>
> > +#include <asm/hypervisor.h>
> > +
> > +int kvm_arch_ptp_init(void)
> > +{
> > + int ret;
> > +
> > + ret =
> kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_KVM_PTP);
> > + if (ret <= 0)
> > + return -EOPNOTSUPP;
> > +
> > + return 0;
> > +}
> > +
> > +int kvm_arch_ptp_get_clock(struct timespec64 *ts) {
> > + ktime_t ktime;
> > + struct arm_smccc_res hvc_res;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + ARM_PTP_NONE_COUNTER, &hvc_res);
>
> I really don't see the need to use a non-architectural counter ID.
> Using the virtual counter ID should just be fine, and shouldn't lead to any
> issue.
>

> Am I missing something?

In this function, no counter data is needed. If virtual counter ID is used here, user may be confused with why we get virtual counter
data and do nothing with it. So I explicitly add a new "NONE" counter ID to make it clear.

WDYT?

Thanks
Jianyong
>
> > + if ((int)(hvc_res.a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + ktime = (u64)hvc_res.a0 << 32 | hvc_res.a1;
>
> Endianness.
>
> > + *ts = ktime_to_timespec64(ktime);
> > +
> > + return 0;
> > +}
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...