Messages in this thread |  | | Subject | Re: [PATCH] cpu-topology: Skip the exist but not possible cpu nodes | From | Dietmar Eggemann <> | Date | Tue, 7 Jan 2020 14:12:17 +0100 |
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On 07/01/2020 02:35, Zengtao (B) wrote: >> -----Original Message----- >> From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com] >> Sent: Tuesday, January 07, 2020 2:42 AM >> To: Zengtao (B); sudeep.holla@arm.com >> Cc: Linuxarm; Greg Kroah-Hartman; Rafael J. Wysocki; >> linux-kernel@vger.kernel.org >> Subject: Re: [PATCH] cpu-topology: Skip the exist but not possible cpu >> nodes >> >> On 02/01/2020 04:24, Zeng Tao wrote: >>> When CONFIG_NR_CPUS is smaller than the cpu nodes defined in the >> device >>> tree, the cpu node parsing will fail. And this is not reasonable for a >>> legal device tree configs. >>> In this patch, skip such cpu nodes rather than return an error. >> >> Is this extra code really necessary? >> >> Currently you get warnings indicating that CONFIG_NR_CPUS is too small >> so you could correct the setup issue easily. >> > > Not only about warning messages, the problem is : > What we are expected to do if the CONFIG_NR_CPUS is too small? I think there > are two choices: > 1. Keep the dts parsing result, but skip the the CPU nodes whose id exceeds the > the CONFIG_NR_CPUS, and this is what this patch do. > 2. Just abort all the CPU nodes parsing, and using MPIDR to guess the topology, > and this is what the current code do.
Ah, you're referring to:
530 void __init init_cpu_topology(void) 531 { ... 540 else if (of_have_populated_dt() && parse_dt_topology()) 541 --> reset_cpu_topology();
With my Juno example (6 Cpus in DT but CONFIG_NR_CPUS=4):
root@juno:~# dmesg | grep "\*\*\|mpidr" [ 0.084760] ** get_cpu_for_node() cpu=1 [ 0.088706] ** get_cpu_for_node() cpu=2 [ 0.092592] ** get_cpu_for_node() cpu=0 [ 0.096550] ** get_cpu_for_node() cpu=3 [ 0.105578] ** get_cpu_for_node() cpu=-19 [ 0.116070] ** store_cpu_topology(): cpuid=0 [ 0.120355] CPU0: cluster 1 core 0 thread -1 mpidr 0x00000080000100 [ 0.242465] ** store_cpu_topology(): cpuid=1 [ 0.242471] CPU1: cluster 0 core 0 thread -1 mpidr 0x00000080000000 [ 0.286505] ** store_cpu_topology(): cpuid=2 [ 0.286510] CPU2: cluster 0 core 1 thread -1 mpidr 0x00000080000001 [ 0.330631] ** store_cpu_topology(): cpuid=3 [ 0.330637] CPU3: cluster 1 core 1 thread -1 mpidr 0x00000080000101
and with your patch:
root@juno:~# dmesg | grep "\*\*\|mpidr" [ 0.084778] ** get_cpu_for_node() cpu=1 [ 0.088742] ** get_cpu_for_node() cpu=2 [ 0.092662] ** get_cpu_for_node() cpu=0 [ 0.096627] ** get_cpu_for_node() cpu=3 [ 0.107942] ** get_cpu_for_node() cpu=-19 [ 0.119429] ** get_cpu_for_node() cpu=-19 [ 0.123461] ** store_cpu_topology(): cpuid=0 [ 0.243571] ** store_cpu_topology(): cpuid=1 [ 0.287610] ** store_cpu_topology(): cpuid=2 [ 0.331737] ** store_cpu_topology(): cpuid=3
so we bail out of store_cpu_topology() since 'cpuid_topo->package_id != -1'.
> And i think choice 1 is better because: > 1. It's a legal dts, we should keep the same result whether CONFIG_NR_CPUS is > too small or not. > 2. In the function of_parse_and_init_cpus, we just do the same way as choice 1. > > But i am open for the issue, any suggestions are welcomed.
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