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

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Date:   Sat, 30 May 2020 19:44:06 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Anchal Agarwal <anchalag@...zon.com>, 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
Subject: Re: [PATCH 09/12] x86/xen: save and restore steal clock

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


>  
> +	/* 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