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From:   Jianyong Wu <Jianyong.Wu@arm.com>
To:     Marc Zyngier <maz@kernel.org>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "yangbo.lu@nxp.com" <yangbo.lu@nxp.com>,
        "john.stultz@linaro.org" <john.stultz@linaro.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
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        Mark Rutland <Mark.Rutland@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Steven Price <Steven.Price@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
        "kvm@vger.kernel.org" <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
Thread-Topic: [RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64
Thread-Index: AQHVrwu1ZTEnzkrQbEOo/hXDFqaU6affG9SAgALmpVCAADyUAIABmc4A
Date:   Fri, 10 Jan 2020 10:15:07 +0000
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Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Thursday, January 9, 2020 5:24 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
>=20
> On 2020-01-09 05:59, Jianyong Wu wrote:
> > 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
> >> >
> >>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> > ^* 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
> >> >
> >>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> > ^* 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
> >> >
> >>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> > * 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 =3D hvc_res.a0 << 32 | hvc_res.a1;
> >> > +	*ts =3D ktime_to_timespec64(ktime_overall);
> >> > +	*cycle =3D 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.
>=20
> See my comment in my reply to patch #6: *Must* seems like a very strong
> word, and you don't explain *why* that's better than just computing the
> total hypercall cost. Hint: given the frequency of the counter (in the fe=
w MHz
> range) vs the frequency of a CPU (in the multiple GHz range, and with an =
IPC
> close enough to 1), I doubt that you'll see the counter making much progr=
ess
> across a hypercall.
>=20
Sorry, I will avoid to use those strong words.

It's really the case that the hypercall won't across cycle in general. But =
sometimes, kernel preempt=20
may happen in the middle of the hypercall which we can't assume how long be=
fore schedule back. so it's better capture them
together at the same time.

> >
> >> > +	*cs =3D &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 =3D hvc_res->a0 << 32 | hvc_res->a1;
> >> > +	*ts =3D 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,
>=20
> Cloud computing? Never heard of that. Will probably never catch on.
>=20
Eh...

> > So we focus it on arm64. Also I have never tested it on arm32 machine
> > ( we lack of arm32 machine)
>=20
> I'm sure your employer can provide you with such a box. I can probably ev=
en
> tell you which cupboard they are stored in... ;-)
>=20
I'm working on building environment for arm32 from now.

> > Do you think it's necessary to enable ptp_kvm on arm32? If so, I can
> > do that.
>=20
> I can't see why we wouldn't, given that it should be a zero effort task (=
none
> of the code here is arch specific).

Ok, I will test it on arm32.
By the way, does nested virtualization diff between arm64 and arm32?

Thanks
Jianyong
>=20
> Thanks,
>=20
>          M.
> --
> Jazz is not dead. It just smells funny...