Messages in this thread | | | Date | Wed, 28 Dec 2005 13:14:02 -0600 | From | Nathan Lynch <> | Subject | Re: [PATCH v2:3/3]Export cpu topology by sysfs |
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> >>What about sane default values for the *_id attributes?
> It depends on the specific architectures. On i386/x86_64, the > default vaules of *_id are 0xffu. On ia64, the default value of > physical_package_id is -1.
> >>For example, > >>say I have a uniprocessor PC without HT or multicore -- should all of > >>these attributes have zero values, or some kind of "special" value to > >>mean "not applicable"? > > This feature is disabled when CONFIG_SMP=n.
Irrelevant. Running SMP kernels on UP boxes is not uncommon.
The point I was trying to make is that these new attributes will show up on systems where they don't provide useful information -- the UP case aside, there are plenty of SMP systems which aren't multicore or multithreaded. We need to take care that the attributes don't provide misleading information on such systems.
> I can't make decision that all arch should use the same default > values, so let architectures to decide. Is it ok?
Not really -- inevitably we'll wind up with an interface that has slightly different semantics on each architecture.
> >>Hmm, why should thread_id be exported at all? Is it useful to > >>userspace in a way that the logical cpu id is not? > > Just to make it clearer. Of course, physical_package_id /core_id/ > logical cpu id could tell enough info like thread id.
Then let's drop thread_id until there's a need for it.
> >>> +static int __cpuinit topology_remove_dev(struct sys_device * sys_dev) > >>> +{ > >>> + sysfs_remove_group(&sys_dev->kobj, &topology_attr_group); > >>> + return 0; > >>> +} > >>> + > >>> +static int __cpuinit topology_cpu_callback(struct notifier_block *nfb, > >>> + unsigned long action, void *hcpu) > >>> +{ > >>> + unsigned int cpu = (unsigned long)hcpu; > >>> + struct sys_device *sys_dev; > >>> + > >>> + sys_dev = get_cpu_sysdev(cpu); > >>> + switch (action) { > >>> + case CPU_ONLINE: > >>> + topology_add_dev(sys_dev); > >>> + break; > >>> + case CPU_DEAD: > >>> + topology_remove_dev(sys_dev); > >>> + break; > >>> + } > >>> + return NOTIFY_OK; > >>> +} > >> > >>I don't think it makes much sense to add and remove the attribute > >>group for cpu online/offline events. The topology information for an > >>offline cpu is potentially valuable -- it could help the admin decide > >>which processor to online at runtime, for example. > >> > >>I believe the correct time to update the topology information is when > >>the topology actually changes (e.g. physical addition or removal of a > >>processor) -- this is independent of online/offline operations. > > Currently, on i386/x86_64/ia64, a cpu gets its own topology by > itself and fills into a global array. If the cpu is offline since > the machine is booted, we can't get its topology info.
Hmm, is this a limitation of those architectures? On ppc64 (where this feature would be applicable) Open Firmware provides such topology information regardless of the cpus' states; does the firmware or ACPI on these platforms not do the same?
> And when a cpu is offline, current kernel deletes it from the > thread_siblings and core_siblings of other cpu.
That's fine -- I'm just arguing against the addition/removal of the attributes when cpus go online and offline.
> >>- This locks us into exporting a three-level topology (thread, core, > >> package), with hard-coded names, when it seems probable that there > >> will be systems with more levels than that in the future. >
> It's easy to add more levels based on my implementations. > Hard-coded names might be a problem. Is there any special > requirement to change the names arch-specifically? If some > architectures really need their specific names, I will change the > names from hard-coded to arch-defined.
No, don't worry about it. I withdraw that objection.
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