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Message-ID: <366387fa507f9c5d5044549cea958ce1@kernel.org>
Date: Mon, 07 Sep 2020 09:54:57 +0100
From: Marc Zyngier <maz@...nel.org>
To: Jianyong Wu <Jianyong.Wu@....com>
Cc: netdev@...r.kernel.org, yangbo.lu@....com, john.stultz@...aro.org,
tglx@...utronix.de, pbonzini@...hat.com,
sean.j.christopherson@...el.com, richardcochran@...il.com,
Mark Rutland <Mark.Rutland@....com>, will@...nel.org,
Suzuki Poulose <Suzuki.Poulose@....com>,
Steven Price <Steven.Price@....com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
Steve Capper <Steve.Capper@....com>,
Justin He <Justin.He@....com>, nd <nd@....com>
Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
On 2020-09-07 09:40, Jianyong Wu wrote:
> Hi Marc,
>
>> -----Original Message-----
>> From: Marc Zyngier <maz@...nel.org>
>> Sent: Saturday, September 5, 2020 7:02 PM
>> To: Jianyong Wu <Jianyong.Wu@....com>
>> Cc: netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org;
>> tglx@...utronix.de; pbonzini@...hat.com;
>> sean.j.christopherson@...el.com;
>> richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>;
>> will@...nel.org; Suzuki Poulose <Suzuki.Poulose@....com>; Steven Price
>> <Steven.Price@....com>; linux-kernel@...r.kernel.org; linux-arm-
>> kernel@...ts.infradead.org; kvmarm@...ts.cs.columbia.edu;
>> kvm@...r.kernel.org; Steve Capper <Steve.Capper@....com>; Justin He
>> <Justin.He@....com>; nd <nd@....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@....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@....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
>> >
>> > 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...
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