Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
From: Marc Zyngier
Date: Mon Sep 07 2020 - 04:55:03 EST
On 2020-09-07 09:40, Jianyong Wu wrote:
Hi Marc,
-----Original Message-----
From: Marc Zyngier <maz@xxxxxxxxxx>
Sent: Saturday, September 5, 2020 7:02 PM
To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
tglx@xxxxxxxxxxxxx; pbonzini@xxxxxxxxxx;
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richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Steven Price
<Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Justin He
<Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
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@xxxxxxx> 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@xxxxxxx>
> ---
> 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
>
> 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>
> +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);
> + if ((long long)(hvc_res.a0) < 0)
> + return -EOPNOTSUPP;
> +
> + ktime = (long long)hvc_res.a0;
> + *ts = ktime_to_timespec64(ktime);
> + *cycle = (long long)hvc_res.a1;
> + *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
> 942f72d8151d..127e96f14f89 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 || ARM64 && ARM_ARCH_TIMER
&&
> +ARM_PSCI_FW
> 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..961abed93dfd
> --- /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_FEATUR
ES_FUNC_ID,
> + &hvc_res);
> + if (!(hvc_res.a0 | BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP)))
> + return -EOPNOTSUPP;
> +
> + return 0;
What happens if the
ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID function isn't
implemented (on an old kernel or a non-KVM hypervisor)? The expected
behaviour is that a0 will contain SMCCC_RET_NOT_SUPPORTED, which is
-1.
The result is that this function always returns "supported". Not an
acceptable
behaviour.
Oh! it's really a stupid mistake, should be "&" not "|".
But even then. (-1 & whatever) is always true.
M.
--
Jazz is not dead. It just smells funny...