Re: [PATCH v2 1/3] xen/sched: introduce cpupool_update_node_affinity()

From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: George Dunlap <george.dunlap@citrix.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 1/3] xen/sched: introduce cpupool_update_node_affinity()
Date: Mon, 15 Aug 2022 13:41:53 +0200	[thread overview]
Message-ID: <9abc061b-2d98-ace8-af4b-0881a5737dd6@suse.com> (raw)
In-Reply-To: <20220815110410.19872-2-jgross@suse.com>

On 15.08.2022 13:04, Juergen Gross wrote:
> For updating the node affinities of all domains in a cpupool add a new
> function cpupool_update_node_affinity().
> 
> In order to avoid multiple allocations of cpumasks carve out memory
> allocation and freeing from domain_update_node_affinity() into new
> helpers, which can be used by cpupool_update_node_affinity().
> 
> Modify domain_update_node_affinity() to take an additional parameter
> for passing the allocated memory in and to allocate and free the memory
> via the new helpers in case NULL was passed.
> 
> This will help later to pre-allocate the cpumasks in order to avoid
> allocations in stop-machine context.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
with the observation that ...

> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -1824,9 +1824,28 @@ int vcpu_affinity_domctl(struct domain *d, uint32_t cmd,
>      return ret;
>  }
>  
> -void domain_update_node_affinity(struct domain *d)
> +bool update_node_aff_alloc(struct affinity_masks *affinity)
>  {
> -    cpumask_var_t dom_cpumask, dom_cpumask_soft;
> +    if ( !alloc_cpumask_var(&affinity->hard) )
> +        return false;
> +    if ( !alloc_cpumask_var(&affinity->soft) )
> +    {
> +        free_cpumask_var(affinity->hard);
> +        return false;
> +    }
> +
> +    return true;
> +}
> +
> +void update_node_aff_free(struct affinity_masks *affinity)
> +{
> +    free_cpumask_var(affinity->soft);
> +    free_cpumask_var(affinity->hard);
> +}
> +
> +void domain_update_node_aff(struct domain *d, struct affinity_masks *affinity)
> +{
> +    struct affinity_masks masks = { };

... the initializer doesn't really look to be needed here, just like
you don't have one in cpupool_update_node_affinity(). The one thing
I'm not sure about is whether old gcc might mis-report a potentially
uninitialized variable with the initializer dropped ...

Jan