linux-kernel - RE: [PATCH] Drivers: hv: util: Implement Time Synchronization using host time sample

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Date:	Fri, 26 Sep 2014 12:30:14 +0000
From:	Thomas Shao <huishao@...rosoft.com>
To:	Mike Surcouf <mps.surcouf.lkml@...il.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	Olaf Hering <olaf@...fle.de>, "Robo Bot" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"KY Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH] Drivers: hv: util: Implement Time Synchronization using
 host time sample


> -----Original Message-----
> From: Mike Surcouf [mailto:mps.surcouf.lkml@...il.com]
> Sent: Friday, September 26, 2014 7:53 PM
> To: Thomas Shao
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> driverdev-devel@...uxdriverproject.org; Olaf Hering; Robo Bot;
> jasowang@...hat.com; KY Srinivasan; Haiyang Zhang
> Subject: Re: [PATCH] Drivers: hv: util: Implement Time Synchronization using
> host time sample
> 
> > +/* helper function to call adjtimex command in user mode */ static
> > +void run_adjtimex_cmd(s64 tickvalue) {
> > +       char *argv[4], *envp[3];
> > +       char str_tickvalue[20];
> > +
> > +       sprintf(str_tickvalue, "%lld", tickvalue);
> > +
> > +       argv[0] = "/sbin/adjtimex";
> > +       argv[1] = "-t";
> > +       argv[2] = str_tickvalue;
> > +       argv[3] = NULL;
> > +
> > +       envp[0] = "HOME=/";
> > +       envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
> > +       envp[2] = NULL;
> > +
> > +       call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC); }
> 
> 
> What happens when adjtimex is not present?
> Is there no kernel space function for that?
> Does this patch affect "not setting correct time on restore" or "not setting
> correct time on  live migration" bug?
> 

If adjtimex is not present, then the slew time part didn't take effect.
There is a kernel space do_adjtmex, but it's only for sys call and not exposed to module. So I didn't use it in my patch.
With this patch, it will step the clock if the time drift is larger than 1 seconds, so it can solve
the issue your mentioned. And on the other hand, "setting correct time on restore" is already fixed
in other patch, which is already in upstream.


> Thanks
> 
> Mike