linux-kernel - Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86

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Message-ID: <20190902182252.GC35858@gmail.com>
Date:   Mon, 2 Sep 2019 20:22:52 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>, dalias@...c.org,
        linux-sh@...r.kernel.org, catalin.marinas@....com,
        dave.hansen@...ux.intel.com, heiko.carstens@...ibm.com,
        linuxarm@...wei.com, jiaxun.yang@...goat.com,
        linux-kernel@...r.kernel.org, mwb@...ux.vnet.ibm.com,
        paulus@...ba.org, hpa@...or.com, sparclinux@...r.kernel.org,
        chenhc@...ote.com, will@...nel.org, linux-s390@...r.kernel.org,
        ysato@...rs.sourceforge.jp, mpe@...erman.id.au, x86@...nel.org,
        rppt@...ux.ibm.com, borntraeger@...ibm.com, dledford@...hat.com,
        mingo@...hat.com, jeffrey.t.kirsher@...el.com,
        benh@...nel.crashing.org, jhogan@...nel.org,
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        akpm@...ux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        davem@...emloft.net,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Sep 02, 2019 at 08:25:24PM +0800, Yunsheng Lin wrote:
> > On 2019/9/2 15:25, Peter Zijlstra wrote:
> > > On Mon, Sep 02, 2019 at 01:46:51PM +0800, Yunsheng Lin wrote:
> > >> On 2019/9/1 0:12, Peter Zijlstra wrote:
> > > 
> > >>> 1) because even it is not set, the device really does belong to a node.
> > >>> It is impossible a device will have magic uniform access to memory when
> > >>> CPUs cannot.
> > >>
> > >> So it means dev_to_node() will return either NUMA_NO_NODE or a
> > >> valid node id?
> > > 
> > > NUMA_NO_NODE := -1, which is not a valid node number. It is also, like I
> > > said, not a valid device location on a NUMA system.
> > > 
> > > Just because ACPI/BIOS is shit, doesn't mean the device doesn't have a
> > > node association. It just means we don't know and might have to guess.
> > 
> > How do we guess the device's location when ACPI/BIOS does not set it?
> 
> See device_add(), it looks to the device's parent and on NO_NODE, puts
> it there.
> 
> Lacking any hints, just stick it to node0 and print a FW_BUG or
> something.
> 
> > It seems dev_to_node() does not do anything about that and leave the
> > job to the caller or whatever function that get called with its return
> > value, such as cpumask_of_node().
> 
> Well, dev_to_node() doesn't do anything; nor should it. It are the
> callers of set_dev_node() that should be taking care.
> 
> Also note how device_add() sets the device node to the parent device's
> node on NUMA_NO_NODE. Arguably we should change it to complain when it
> finds NUMA_NO_NODE and !parent.
> 
> ---
>  drivers/base/core.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f0dd8e38fee3..2caf204966a0 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2120,8 +2120,16 @@ int device_add(struct device *dev)
>  		dev->kobj.parent = kobj;
>  
>  	/* use parent numa_node */
> -	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
> -		set_dev_node(dev, dev_to_node(parent));
> +	if (dev_to_node(dev) == NUMA_NO_NODE) {
> +		if (parent)
> +			set_dev_node(dev, dev_to_node(parent));
> +#ifdef CONFIG_NUMA
> +		else {
> +			pr_err("device: '%s': has no assigned NUMA node\n", dev_name(dev));
> +			set_dev_node(dev, 0);
> +		}
> +#endif

BTW., is firmware required to always provide a NUMA node on NUMA systems?

I.e. do we really want this warning on non-NUMA systems that don't assign 
NUMA nodes?

Also, even on NUMA systems, is firmware required to provide a NUMA node - 
i.e. is it in principle invalid to offer no NUMA binding?

Thanks,

	Ingo