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Date: Sat, 28 Jan 2017 19:04:55 +0000
From: KY Srinivasan <kys@...rosoft.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>,
"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
CC: Thomas Gleixner <tglx@...utronix.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Haiyang Zhang <haiyangz@...rosoft.com>,
"John Stultz" <john.stultz@...aro.org>,
"Alex Ng (LIS)" <alexng@...rosoft.com>,
Stephen Hemminger <stephen@...workplumber.org>,
Olaf Hering <olaf@...fle.de>,
Richard Cochran <richardcochran@...il.com>,
Radim Krcmar <rkrcmar@...hat.com>
Subject: RE: [PATCH v4 2/2] hv_utils: implement Hyper-V PTP source
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Thursday, January 19, 2017 6:17 AM
> To: devel@...uxdriverproject.org
> Cc: Thomas Gleixner <tglx@...utronix.de>; linux-kernel@...r.kernel.org;
> Haiyang Zhang <haiyangz@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>; John Stultz <john.stultz@...aro.org>; Alex Ng (LIS)
> <alexng@...rosoft.com>; Stephen Hemminger
> <stephen@...workplumber.org>; Olaf Hering <olaf@...fle.de>; Richard
> Cochran <richardcochran@...il.com>; Radim Krcmar
> <rkrcmar@...hat.com>
> Subject: [PATCH v4 2/2] hv_utils: implement Hyper-V PTP source
>
> With TimeSync version 4 protocol support we started updating system time
> continuously through the whole lifetime of Hyper-V guests. Every 5 seconds
> there is a time sample from the host which triggers do_settimeofday[64]().
> While the time from the host is very accurate such adjustments may cause
> issues:
> - Time is jumping forward and backward, some applications may misbehave.
> - In case an NTP server runs in parallel and uses something else for time
> sync (network, PTP,...) system time will never converge.
> - Systemd starts annoying you by printing "Time has been changed" every 5
> seconds to the system log.
>
> Instead of doing in-kernel time adjustments offload the work to an
> NTP client by exposing TimeSync messages as a PTP device. Users may now
> decide what they want to use as a source.
>
> I tested the solution with chrony, the config was:
>
> refclock PHC /dev/ptp0 poll 3 precision 1e-9
>
> The result I'm seeing is accurate enough, the time delta between the guest
> and the host is almost always within [-10us, +10us], the in-kernel solution
> was giving us comparable results.
>
> I also tried implementing PPS device instead of PTP by using not currently
> used Hyper-V synthetic timers (we use only one of four for clockevent) but
> with PPS source only chrony wasn't able to give me the required accuracy,
> the delta often more that 100us.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Vitaly,
This patch does not apply. Please rebase and send.
K. Y
> ---
> drivers/hv/hv_util.c | 144
> ++++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 119 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index 94719eb..e1211b8 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -27,6 +27,7 @@
> #include <linux/sysctl.h>
> #include <linux/reboot.h>
> #include <linux/hyperv.h>
> +#include <linux/ptp_clock_kernel.h>
>
> #include "hyperv_vmbus.h"
>
> @@ -179,31 +180,34 @@ struct adj_time_work {
> u8 flags;
> };
>
> +static u64 get_timeadj_latency(u64 ref_time)
> +{
> + u64 current_tick;
> +
> + if (ts_srv_version <= TS_VERSION_3)
> + return 0;
> +
> + /*
> + * Some latency has been introduced since Hyper-V generated
> + * its time sample. Take that latency into account before
> + * using TSC reference time sample from Hyper-V.
> + *
> + * This sample is given by TimeSync v4 and above hosts.
> + */
> + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
> + return current_tick - ref_time;
> +}
> +
> static void hv_set_host_time(struct work_struct *work)
> {
> struct adj_time_work *wrk;
> - s64 host_tns;
> - u64 newtime;
> struct timespec64 host_ts;
> + u64 newtime;
>
> wrk = container_of(work, struct adj_time_work, work);
>
> - newtime = wrk->host_time;
> - if (ts_srv_version > TS_VERSION_3) {
> - /*
> - * Some latency has been introduced since Hyper-V
> generated
> - * its time sample. Take that latency into account before
> - * using TSC reference time sample from Hyper-V.
> - *
> - * This sample is given by TimeSync v4 and above hosts.
> - */
> - u64 current_tick;
> -
> - rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
> - newtime += (current_tick - wrk->ref_time);
> - }
> - host_tns = (newtime - WLTIMEDELTA) * 100;
> - host_ts = ns_to_timespec64(host_tns);
> + newtime = wrk->host_time + get_timeadj_latency(wrk->ref_time);
> + host_ts = ns_to_timespec64((newtime - WLTIMEDELTA) * 100);
>
> do_settimeofday64(&host_ts);
> }
> @@ -222,22 +226,52 @@ static void hv_set_host_time(struct work_struct
> *work)
> * to discipline the clock.
> */
> static struct adj_time_work wrk;
> -static inline void adj_guesttime(u64 hosttime, u64 reftime, u8 flags)
> +
> +/*
> + * The last time sample, received from the host. PTP device responds to
> + * requests by using this data and the current partition-wide time reference
> + * count.
> + */
> +static struct {
> + u64 host_time;
> + u64 ref_time;
> + spinlock_t lock;
> +} host_ts;
> +
> +static inline void adj_guesttime(u64 hosttime, u64 reftime, u8 adj_flags)
> {
> + unsigned long flags;
>
> /*
> * This check is safe since we are executing in the
> * interrupt context and time synch messages arre always
> * delivered on the same CPU.
> */
> - if (work_pending(&wrk.work))
> - return;
> + if (adj_flags & ICTIMESYNCFLAG_SYNC) {
> + if (work_pending(&wrk.work))
> + return;
>
> - wrk.host_time = hosttime;
> - wrk.ref_time = reftime;
> - wrk.flags = flags;
> - if ((flags & (ICTIMESYNCFLAG_SYNC | ICTIMESYNCFLAG_SAMPLE)) !=
> 0) {
> + wrk.host_time = hosttime;
> + wrk.ref_time = reftime;
> + wrk.flags = adj_flags;
> schedule_work(&wrk.work);
> + } else {
> + spin_lock_irqsave(&host_ts.lock, flags);
> + host_ts.host_time = hosttime;
> +
> + /*
> + * Prior to version 4 TimeSync messages from the host don't
> + * contain any reference time (the time when the time
> sample
> + * was generated), save the current time reference count
> + * instead. This adds a small delta between the time sample
> + * generation and the reception of the sample here to the
> result
> + * but it's the best thing we can do.
> + */
> + if (ts_srv_version <= TS_VERSION_3)
> + rdmsrl(HV_X64_MSR_TIME_REF_COUNT,
> host_ts.ref_time);
> + else
> + host_ts.ref_time = reftime;
> + spin_unlock_irqrestore(&host_ts.lock, flags);
> }
> }
>
> @@ -470,14 +504,74 @@ static struct hv_driver util_drv = {
> .remove = util_remove,
> };
>
> +static int hv_ptp_enable(struct ptp_clock_info *info,
> + struct ptp_clock_request *request, int on)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static int hv_ptp_settime(struct ptp_clock_info *p, const struct timespec64
> *ts)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static int hv_ptp_adjfreq(struct ptp_clock_info *ptp, s32 delta)
> +{
> + return -EOPNOTSUPP;
> +}
> +static int hv_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static int hv_ptp_gettime(struct ptp_clock_info *info, struct timespec64
> *ts)
> +{
> + u64 newtime;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&host_ts.lock, flags);
> + newtime = host_ts.host_time +
> get_timeadj_latency(host_ts.ref_time);
> + *ts = ns_to_timespec64((newtime - WLTIMEDELTA) * 100);
> + spin_unlock_irqrestore(&host_ts.lock, flags);
> +
> + return 0;
> +}
> +
> +static const struct ptp_clock_info ptp_hyperv_info = {
> + .name = "hyperv",
> + .enable = hv_ptp_enable,
> + .adjtime = hv_ptp_adjtime,
> + .adjfreq = hv_ptp_adjfreq,
> + .gettime64 = hv_ptp_gettime,
> + .settime64 = hv_ptp_settime,
> + .owner = THIS_MODULE,
> +};
> +
> +static struct ptp_clock *hv_ptp_clock;
> +
> static int hv_timesync_init(struct hv_util_service *srv)
> {
> INIT_WORK(&wrk.work, hv_set_host_time);
> +
> + /*
> + * ptp_clock_register() returns NULL when
> CONFIG_PTP_1588_CLOCK is
> + * disabled but the driver is still useful without the PTP device
> + * as it still handles the ICTIMESYNCFLAG_SYNC case.
> + */
> + hv_ptp_clock = ptp_clock_register(&ptp_hyperv_info, NULL);
> + if (IS_ERR_OR_NULL(hv_ptp_clock)) {
> + pr_err("cannot register PTP clock: %ld\n",
> + PTR_ERR(hv_ptp_clock));
> + hv_ptp_clock = NULL;
> + }
> +
> return 0;
> }
>
> static void hv_timesync_deinit(void)
> {
> + if (hv_ptp_clock)
> + ptp_clock_unregister(hv_ptp_clock);
> cancel_work_sync(&wrk.work);
> }
>
> --
> 2.9.3
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