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Re: [PATCH v4 03/17] xen/arm: implement node distance helpers for Arm
- To: Henry Wang <Henry.Wang@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 25 Apr 2023 11:43:08 +0200
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- Cc: Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 25 Apr 2023 09:43:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.04.2023 11:31, Henry Wang wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> On 25.04.2023 09:56, Henry Wang wrote:
>>> + /* NUMA defines NUMA_NO_DISTANCE as unreachable and 0-9 are
>> undefined */
>>> + if ( distance >= NUMA_NO_DISTANCE || 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;
>>> + }
>>
>> I appreciate the checking that node-local references are
>> NUMA_LOCAL_DISTANCE,
>> but if they're wrongly passed into here, shouldn't the resulting array still
>> have NUMA_LOCAL_DISTANCE on its diagonal, at least as far as present nodes
>> go?
>
> Apologies in advance to ask more specific details from you as I am not sure
> if I can correctly understand the "if they're wrongly passed into here" case.
> Do you
> mean we are always guaranteed that if from == to, the distance will always be
> NUMA_LOCAL_DISTANCE so the (from == to && distance != NUMA_LOCAL_DISTANCE)
> check is redundant and can be removed? Thanks.
It's a little odd that you ask me: It is your code which insists on
NUMA_LOCAL_DISTANCE when from == to. If you insist on your caller to pass
only this one value, then I think it is only logical to also set the
respective table entries to that value (rather than leaving them at
NUMA_NO_DISTANCE).
Jan
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