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

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Message-ID: <20190902125644.GQ2369@hirez.programming.kicks-ass.net>
Date:   Mon, 2 Sep 2019 14:56:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     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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        linux-alpha@...r.kernel.org, bp@...en8.de,
        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

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
+	}
 
 	/* first, register with generic layer. */
 	/* we require the name to be set before, and pass NULL */