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Sat, 05 Sep 2020 12:33:23 +0100 Date: Sat, 05 Sep 2020 12:33:22 +0100 Message-ID: <871rjgmpa5.wl-maz@kernel.org> From: Marc Zyngier To: Jianyong Wu Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 In-Reply-To: <20200904092744.167655-9-jianyong.wu@arm.com> References: <20200904092744.167655-1-jianyong.wu@arm.com> <20200904092744.167655-9-jianyong.wu@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26.3 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: jianyong.wu@arm.com, 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@arm.com, will@kernel.org, suzuki.poulose@arm.com, 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@arm.com, justin.he@arm.com, nd@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200905_073326_969441_814635A5 X-CRM114-Status: GOOD ( 32.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark.Rutland@arm.com, justin.he@arm.com, kvm@vger.kernel.org, suzuki.poulose@arm.com, netdev@vger.kernel.org, richardcochran@gmail.com, Steve.Capper@arm.com, linux-kernel@vger.kernel.org, sean.j.christopherson@intel.com, steven.price@arm.com, john.stultz@linaro.org, yangbo.lu@nxp.com, pbonzini@redhat.com, tglx@linutronix.de, nd@arm.com, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 04 Sep 2020 10:27:42 +0100, Jianyong Wu 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 > --- > 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 And I missed that one earlier: > 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 No conditional includes, please. > +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_FUNC_ID, > + ARM_PTP_VIRT_COUNTER, &hvc_res); You don't need to assume anything. This driver already provides you with the information you need to tell the hypervisor which counter to use: if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) ptp_counter = ARM_PTP_VIRT_COUNTER; else ptp_counter = ARM_PTP_PHYS_COUNTER; arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID, ptp_counter, &hvc_res); At least, this is vaguely future proof. The hypervisor will still have to discriminate between a call between a call from vEL1 or vEL2 to decide whether to subtract the offset from the counter value, but that's out of scope for now. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel