RE: [PATCH 23/37] xen/arm: implement node distance helpers for Arm

[Wei Chen <Wei.Chen@arm.com>]

Hi Stefano,

> -----Original Message-----
> From: Stefano Stabellini <sstabellini@kernel.org>
> Sent: 2021年9月24日 9:47
> To: Wei Chen <Wei.Chen@arm.com>
> Cc: xen-devel@lists.xenproject.org; sstabellini@kernel.org; julien@xen.org;
> Bertrand Marquis <Bertrand.Marquis@arm.com>
> Subject: Re: [PATCH 23/37] xen/arm: implement node distance helpers for
> Arm
> 
> On Thu, 23 Sep 2021, Wei Chen wrote:
> > We will parse NUMA nodes distances from device tree or ACPI
> > table. So we need a matrix to record the distances between
> > any two nodes we parsed. Accordingly, we provide this
> > node_set_distance API for device tree or ACPI table parsers
> > to set the distance for any two nodes in this patch.
> > When NUMA initialization failed, __node_distance will return
> > NUMA_REMOTE_DISTANCE, this will help us avoid doing rollback
> > for distance maxtrix when NUMA initialization failed.
> >
> > Signed-off-by: Wei Chen <wei.chen@arm.com>
> > ---
> >  xen/arch/arm/Makefile      |  1 +
> >  xen/arch/arm/numa.c        | 69 ++++++++++++++++++++++++++++++++++++++
> >  xen/include/asm-arm/numa.h | 13 +++++++
> >  3 files changed, 83 insertions(+)
> >  create mode 100644 xen/arch/arm/numa.c
> >
> > diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> > index ae4efbf76e..41ca311b6b 100644
> > --- a/xen/arch/arm/Makefile
> > +++ b/xen/arch/arm/Makefile
> > @@ -35,6 +35,7 @@ obj-$(CONFIG_LIVEPATCH) += livepatch.o
> >  obj-y += mem_access.o
> >  obj-y += mm.o
> >  obj-y += monitor.o
> > +obj-$(CONFIG_NUMA) += numa.o
> >  obj-y += p2m.o
> >  obj-y += percpu.o
> >  obj-y += platform.o
> > diff --git a/xen/arch/arm/numa.c b/xen/arch/arm/numa.c
> > new file mode 100644
> > index 0000000000..3f08870d69
> > --- /dev/null
> > +++ b/xen/arch/arm/numa.c
> > @@ -0,0 +1,69 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Arm Architecture support layer for NUMA.
> > + *
> > + * Copyright (C) 2021 Arm Ltd
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> > + *
> > + */
> > +#include <xen/init.h>
> > +#include <xen/numa.h>
> > +
> > +static uint8_t __read_mostly
> > +node_distance_map[MAX_NUMNODES][MAX_NUMNODES] = {
> > +    { 0 }
> > +};
> > +
> > +void __init numa_set_distance(nodeid_t from, nodeid_t to, uint32_t
> distance)
> > +{
> > +    if ( from >= MAX_NUMNODES || to >= MAX_NUMNODES )
> > +    {
> > +        printk(KERN_WARNING
> > +               "NUMA: invalid nodes: from=%"PRIu8" to=%"PRIu8"
> MAX=%"PRIu8"\n",
> > +               from, to, MAX_NUMNODES);
> > +        return;
> > +    }
> > +
> > +    /* NUMA defines 0xff as an unreachable node and 0-9 are undefined
> */
> > +    if ( distance >= NUMA_NO_DISTANCE ||
> > +        (distance >= NUMA_DISTANCE_UDF_MIN &&
> > +         distance <= NUMA_DISTANCE_UDF_MAX) ||
> > +        (from == to && distance != NUMA_LOCAL_DISTANCE) )
> > +    {
> > +        printk(KERN_WARNING
> > +               "NUMA: invalid distance: from=%"PRIu8" to=%"PRIu8"
> distance=%"PRIu32"\n",
> > +               from, to, distance);
> > +        return;
> > +    }
> > +
> > +    node_distance_map[from][to] = distance;
> > +}
> > +
> > +uint8_t __node_distance(nodeid_t from, nodeid_t to)
> > +{
> > +    /* When NUMA is off, any distance will be treated as remote. */
> > +    if ( srat_disabled() )
> 
> Given that this is ARM specific code and specific to ACPI, I don't think
> we should have any call to something called "srat_disabled".
> 
> I suggest to either rename srat_disabled to numa_distance_disabled.
> 
> Other than that, this patch looks OK to me.
> 

srat stands for static resource affinity table, I think dtb also can be
treated as a static resource affinity table. So I keep SRAT in this patch
and other patches. I have seen your comment in patch#25. Before x86 maintainers
give any feedback, can we still keep srat here?

> 
> > +        return NUMA_REMOTE_DISTANCE;
> > +
> > +    /*
> > +     * Check whether the nodes are in the matrix range.
> > +     * When any node is out of range, except from and to nodes are the
> > +     * same, we treat them as unreachable (return 0xFF)
> > +     */
> > +    if ( from >= MAX_NUMNODES || to >= MAX_NUMNODES )
> > +        return from == to ? NUMA_LOCAL_DISTANCE : NUMA_NO_DISTANCE;
> > +
> > +    return node_distance_map[from][to];
> > +}
> > +EXPORT_SYMBOL(__node_distance);
> > diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h
> > index 21569e634b..758eafeb05 100644
> > --- a/xen/include/asm-arm/numa.h
> > +++ b/xen/include/asm-arm/numa.h
> > @@ -9,8 +9,21 @@ typedef u8 nodeid_t;
> >
> >  #ifdef CONFIG_NUMA
> >
> > +/*
> > + * In ACPI spec, 0-9 are the reserved values for node distance,
> > + * 10 indicates local node distance, 20 indicates remote node
> > + * distance. Set node distance map in device tree will follow
> > + * the ACPI's definition.
> > + */
> > +#define NUMA_DISTANCE_UDF_MIN   0
> > +#define NUMA_DISTANCE_UDF_MAX   9
> > +#define NUMA_LOCAL_DISTANCE     10
> > +#define NUMA_REMOTE_DISTANCE    20
> > +
> >  #define NR_NODE_MEMBLKS NR_MEM_BANKS
> >
> > +extern void numa_set_distance(nodeid_t from, nodeid_t to, uint32_t
> distance);
> > +
> >  #else
> >
> >  /* Fake one node for now. See also node_online_map. */
> > --
> > 2.25.1
> >