linux-kernel - Re: [PATCH 09/12] x86/xen: save and restore steal clock

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Message-ID: <20200604183336.GA25251@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com>
Date:   Thu, 4 Jun 2020 18:33:36 +0000
From:   Anchal Agarwal <anchalag@...zon.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <hpa@...or.com>, <x86@...nel.org>, <jgross@...e.com>,
        <linux-pm@...r.kernel.org>, <linux-mm@...ck.org>,
        <kamatam@...zon.com>, <sstabellini@...nel.org>,
        <konrad.wilk@...cle.com>, <roger.pau@...rix.com>,
        <axboe@...nel.dk>, <davem@...emloft.net>, <rjw@...ysocki.net>,
        <len.brown@...el.com>, <pavel@....cz>, <peterz@...radead.org>,
        <eduval@...zon.com>, <sblbir@...zon.com>,
        <xen-devel@...ts.xenproject.org>, <vkuznets@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dwmw@...zon.co.uk>, <benh@...nel.crashing.org>,
        <anchalag@...zon.com>
Subject: Re: [PATCH 09/12] x86/xen: save and restore steal clock

On Sat, May 30, 2020 at 07:44:06PM -0400, Boris Ostrovsky wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> On 5/19/20 7:28 PM, Anchal Agarwal wrote:
> > From: Munehisa Kamata <kamatam@...zon.com>
> >
> > Save steal clock values of all present CPUs in the system core ops
> > suspend callbacks. Also, restore a boot CPU's steal clock in the system
> > core resume callback. For non-boot CPUs, restore after they're brought
> > up, because runstate info for non-boot CPUs are not active until then.
> >
> > Signed-off-by: Munehisa Kamata <kamatam@...zon.com>
> > Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
> > ---
> >  arch/x86/xen/suspend.c | 13 ++++++++++++-
> >  arch/x86/xen/time.c    |  3 +++
> >  2 files changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> > index 784c4484100b..dae0f74f5390 100644
> > --- a/arch/x86/xen/suspend.c
> > +++ b/arch/x86/xen/suspend.c
> > @@ -91,12 +91,20 @@ void xen_arch_suspend(void)
> >  static int xen_syscore_suspend(void)
> >  {
> >       struct xen_remove_from_physmap xrfp;
> > -     int ret;
> > +     int cpu, ret;
> >
> >       /* Xen suspend does similar stuffs in its own logic */
> >       if (xen_suspend_mode_is_xen_suspend())
> >               return 0;
> >
> > +     for_each_present_cpu(cpu) {
> > +             /*
> > +              * Nonboot CPUs are already offline, but the last copy of
> > +              * runstate info is still accessible.
> > +              */
> > +             xen_save_steal_clock(cpu);
> > +     }
> > +
> >       xrfp.domid = DOMID_SELF;
> >       xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
> >
> > @@ -118,6 +126,9 @@ static void xen_syscore_resume(void)
> >
> >       pvclock_resume();
> 
> 
> Doesn't make any difference but I think since this patch is where you
> are dealing with clock then pvclock_resume() should be added here and
> not in the earlier patch.
> 
> 
> -boris
I think the reason it may be in previous patch because it was a part
of syscore_resume and steal clock fix came in later. 
It could me moved to this patch that deals with all clock stuff.

-Anchal
> 
> 

> >
> > +     /* Nonboot CPUs will be resumed when they're brought up */
> > +     xen_restore_steal_clock(smp_processor_id());
> > +
> >       gnttab_resume();
> >  }
> >
> > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> > index c8897aad13cd..33d754564b09 100644
> > --- a/arch/x86/xen/time.c
> > +++ b/arch/x86/xen/time.c
> > @@ -545,6 +545,9 @@ static void xen_hvm_setup_cpu_clockevents(void)
> >  {
> >       int cpu = smp_processor_id();
> >       xen_setup_runstate_info(cpu);
> > +     if (cpu)
> > +             xen_restore_steal_clock(cpu);
> > +
> >       /*
> >        * xen_setup_timer(cpu) - snprintf is bad in atomic context. Hence
> >        * doing it xen_hvm_cpu_notify (which gets called by smp_init during
> 
> 
>