Messages in this thread | | | Date | Mon, 11 Aug 2008 11:28:24 -0700 | From | Max Krasnyansky <> | Subject | Re: [PATCH] Resurect proper handling of maxcpus= kernel option |
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Ingo Molnar wrote: > * Max.Krasnyansky@qualcomm.com <Max.Krasnyansky@qualcomm.com> wrote: > >> From: Max Krasnyansky <maxk@qualcomm.com> >> >> For some reason we had redundant parsers registered for maxcpus=. One >> in init/main.c and another in arch/x86/smpboot.c So I nuked the one in >> arch/x86. >> >> Also 64-bit kernels used to handle maxcpus= as documented in >> Documentation/cpu-hotplug.txt. CPUs with 'id > maxcpus' are >> initialized but not booted. 32-bit version for some reason ignored >> them even though all the infrastructure for booting them later is >> there. >> >> In the current mainline both 64 and 32 bit versions are broken. I'm >> too lazy to look through git history but I'm guessing it happened as >> part of the i386 and x86_64 unification. > > yes in essence. 32-bit always had maxcpus as a hard restriction in the > number of CPUs. This got extended to 64-bit as well, via commit > 89b08200ad: > > x86: make x86_64 accept the max_cpus parameter > > in v2.6.25. Two major kernel releases and nobody noticed - it's a rarely > used option. > >> This patch restores the correct behaviour. I've tested x86_64 version >> on 4- and 8- way Core2 and 2-way Opteron based machines. Various >> config combinations SMP, !SMP, CPU_HOTPLUG, !CPU_HOTPLUG. Booted with >> maxcpus=1 and maxcpus=4, etc. Everything is working as expected. >> >> I cannot test 32-bit version (no 32-bit machines here). > > This will need some test time on 32-bit as that is where this represents > a material change. ( albeit what matters most is the maxcpus=1 > distinction - and for that nosmp can be used as well to turn off > multi-cpu support altogether. So we could do this in v2.6.27 as well. )
So far we got a couple of reports that it works as expected on 32 (both laptop and server/desktop).
> Also, a quick grep shows that your patch will very likely break the > visws build: > > arch/x86/kernel/visws_quirks.c:extern unsigned int __cpuinitdata maxcpus; > arch/x86/kernel/visws_quirks.c: if (ncpus > maxcpus) > arch/x86/kernel/visws_quirks.c: ncpus = maxcpus; > > could you please fix that?
Oh. I missed that one. Will fix.
Max
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