Messages in this thread | | | Date | Thu, 09 Jan 2020 09:24:20 +0000 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64 |
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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 >> > >> ========================================================== >> ============== >> > ^* 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 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 = hvc_res.a0 << 32 | hvc_res.a1; >> > + *ts = ktime_to_timespec64(ktime_overall); >> > + *cycle = 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.
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 few 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 progress across a hypercall.
> >> > + *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 >> > 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 = hvc_res->a0 << 32 | hvc_res->a1; >> > + *ts = 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,
Cloud computing? Never heard of that. Will probably never catch on.
> So we focus it on arm64. Also I have never tested it on arm32 machine > ( we lack of arm32 machine)
I'm sure your employer can provide you with such a box. I can probably even tell you which cupboard they are stored in... ;-)
> Do you think it's necessary to enable ptp_kvm on arm32? If so, I can do > that.
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).
Thanks,
M. -- Jazz is not dead. It just smells funny...
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