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From: | Gavin Shan |
Subject: | Re: [PATCH 1/2] numa: Set default distance map if needed |
Date: | Wed, 13 Oct 2021 09:59:05 +1100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 |
Hi Drew and Igor, On 10/13/21 12:05 AM, Andrew Jones wrote:
On Tue, Oct 12, 2021 at 02:34:30PM +0200, Igor Mammedov wrote:On Tue, 12 Oct 2021 13:48:02 +0200On Tue, Oct 12, 2021 at 09:31:55PM +1100, Gavin Shan wrote:On 10/12/21 8:40 PM, Igor Mammedov wrote:On Wed, 6 Oct 2021 18:22:08 +0800 Gavin Shan <gshan@redhat.com> wrote:The following option is used to specify the distance map. It's possible the option isn't provided by user. In this case, the distance map isn't populated and exposed to platform. On the other hand, the empty NUMA node, where no memory resides, is allowed on ARM64 virt platform. For these empty NUMA nodes, their corresponding device-tree nodes aren't populated, but their NUMA IDs should be included in the "/distance-map" device-tree node, so that kernel can probe them properly if device-tree is used. -numa,dist,src=<numa_id>,dst=<numa_id>,val=<distance> So when user doesn't specify distance map, we need to generate the default distance map, where the local and remote distances are 10 and 20 separately. This adds an extra parameter to the exiting complete_init_numa_distance() to generate the default distance map for this case. Signed-off-by: Gavin Shan <gshan@redhat.com>how about error-ing out if distance map is required but not provided by user explicitly and asking user to fix command line? Reasoning behind this that defaults are hard to maintain and will require compat hacks and being raod blocks down the road. Approach I was taking with generic NUMA code, is deprecating defaults and replacing them with sanity checks, which bail out on incorrect configuration and ask user to correct command line. Hence I dislike approach taken in this patch. If you really wish to provide default, push it out of generic code into ARM specific one (then I won't oppose it that much (I think PPC does some magic like this)) Also behavior seems to be ARM specific so generic NUMA code isn't a place for it anywaysThanks for your comments. Yep, Lets move the logic into hw/arm/virt in v3 because I think simply error-ing out will block the existing configuration where the distance map isn't provided by user. After moving the logic to hw/arm/virt, this patch is consistent with PATCH[02/02] and the specific platform is affected only.Please don't move anything NUMA DT generic to hw/arm/virt. If the spec isn't arch-specific, then the modeling shouldn't be either.If you want to error-out for all configs missing the distance map, then you'll need compat code.If you only want to error-out for configs that have empty NUMA nodes and are missing a distance map, then you don't need compat code, because those configs never worked before anyway.I think memory-less configs without distance map worked for x86 just fine.Ah, yes, we should make the condition for erroring-out be have-memoryless-nodes && !have-distance-map && generate-DT ACPI only architectures, x86, don't need to care about this.
Sure, I will change the code accordingly in v3. Thanks for discussing it through with Igor :)
After looking at this thread all over again it seems to me that using distance map as a source of numa ids is a mistake.You'll have to discuss that with Rob Herring, as that was his proposal. He'll expect a counterproposal though, which we don't have...
However, Getting the NUMA node IDs from PCI host bridge and CPUs aren't working out. I will explain in another thread. Thanks, Gavin
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