From: Marc Zyngier <maz@kernel.org>
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>,
Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
Date: Mon, 07 Sep 2020 09:54:57 +0100 [thread overview]
Message-ID: <366387fa507f9c5d5044549cea958ce1@kernel.org> (raw)
In-Reply-To: <HE1PR0802MB2555CC56351616836A95FB19F4280@HE1PR0802MB2555.eurprd08.prod.outlook.com>
On 2020-09-07 09:40, Jianyong Wu wrote:
> Hi Marc,
>
>> -----Original Message-----
>> From: Marc Zyngier <maz@kernel.org>
>> Sent: Saturday, September 5, 2020 7:02 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>; Justin He
>> <Justin.He@arm.com>; nd <nd@arm.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@arm.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@arm.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...
next prev parent reply other threads:[~2020-09-07 8:55 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 9:27 [PATCH v14 00/10] Enable ptp_kvm for arm64 Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 01/10] arm64: Probe for the presence of KVM hypervisor services during boot Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 02/10] arm/arm64: KVM: Advertise KVM UID to guests via SMCCC Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 03/10] smccc: Export smccc conduit get helper Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 04/10] ptp: Reorganize ptp_kvm module to make it arch-independent Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 05/10] time: Add mechanism to recognize clocksource in time_get_snapshot Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 06/10] clocksource: Add clocksource id for arm arch counter Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 07/10] arm64/kvm: Add hypercall service for kvm ptp Jianyong Wu
2020-09-04 16:15 ` Marc Zyngier
2020-09-07 8:10 ` Jianyong Wu
2020-09-05 11:04 ` Marc Zyngier
2020-09-07 8:13 ` Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 Jianyong Wu
2020-09-05 11:01 ` Marc Zyngier
2020-09-06 10:00 ` Marc Zyngier
2020-09-07 8:40 ` Jianyong Wu
2020-09-07 8:54 ` Marc Zyngier [this message]
2020-09-07 9:28 ` Jianyong Wu
2020-09-07 9:47 ` Marc Zyngier
2020-09-07 10:11 ` Jianyong Wu
2020-09-05 11:33 ` Marc Zyngier
2020-09-07 8:51 ` Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 09/10] doc: add ptp_kvm introduction for arm64 support Jianyong Wu
2020-09-04 16:18 ` Marc Zyngier
2020-09-07 7:55 ` Jianyong Wu
2020-09-04 9:27 ` [PATCH v14 10/10] arm64: Add kvm capability check extension for ptp_kvm Jianyong Wu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=366387fa507f9c5d5044549cea958ce1@kernel.org \
--to=maz@kernel.org \
--cc=Jianyong.Wu@arm.com \
--cc=Justin.He@arm.com \
--cc=Mark.Rutland@arm.com \
--cc=Steve.Capper@arm.com \
--cc=Steven.Price@arm.com \
--cc=Suzuki.Poulose@arm.com \
--cc=john.stultz@linaro.org \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=nd@arm.com \
--cc=netdev@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=richardcochran@gmail.com \
--cc=sean.j.christopherson@intel.com \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
--cc=yangbo.lu@nxp.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).