linux-kernel - Re: [PATCH 1/2] keep guest wallclock in sync with host clock

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Message-ID: <4A9E5A8B.4060804@redhat.com>
Date:	Wed, 02 Sep 2009 14:44:11 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] keep guest wallclock in sync with host clock

On 09/01/2009 02:50 PM, Glauber Costa wrote:
> KVM clock is great to avoid drifting in guest VMs running ontop of kvm.
> However, the current mechanism will not propagate changes in wallclock value
> upwards. This effectively means that in a large pool of VMs that need accurate timing,
> all of them has to run NTP, instead of just the host doing it.
>
> Since the host updates information in the shared memory area upon msr writes,
> this patch introduces a worker that writes to that msr, and calls do_settimeofday
> at fixed intervals, with second resolution. A interval of 0 determines that we
> are not interested in this behaviour. A later patch will make this optional at
> runtime
>
> +
> +static void kvm_sync_wall_clock(struct work_struct *work)
> +{
> +	struct timespec now;
> +
> +	kvm_get_wall_ts(&now);
>    

What happens if we schedule here?

> +
> +	do_settimeofday(&now);
> +	schedule_next_update();
> +}
> +
> +static __init int init_updates(void)
> +{
> +	schedule_next_update();
> +	return 0;
> +}
> +/*
> + * It has to be run after workqueues are initialized, since we call
> + * schedule_delayed_work. Other than that, we have no specific requirements
> + */
> +late_initcall(init_updates);
>    

Should this run on bare metal too?

-- 
error compiling committee.c: too many arguments to function

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