Messages in this thread | | | Date | Mon, 17 Feb 2014 15:16:26 +0100 | From | Petr Tesarik <> | Subject | Re: [PATCH] x86: Issue a warning if number of present CPUs > maxcpus and CONFIG_HOTPLUG=n |
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On Mon, 17 Feb 2014 10:40:07 -0300 Henrique de Moraes Holschuh <hmh@hmh.eng.br> wrote:
> On Mon, 17 Feb 2014, Petr Tesarik wrote: > > Well, if the user passes both nr_cpus and maxcpus parameters to the > > kernel, I think it's fair to issue two warnings. But if everyone agrees > > that only the maxcpus warning should be printed in that case, I can > > send a version 2 of my patch. > > Please remember that the market is full of motherboards with the extremely > annoying behaviour of declaring ACPI objects for CPU cores that will never > be available. This includes a large number of workstation and server boards > at the very least, from at least one rather large vendor. > > As far as I know, we still don't have a way to realiably detect this and get > rid of the ghost processors which will *NEVER* become online. Setting > maxcpus or nr_cpus manually is the current way to avoid wasting runtime > resources because of phantom cores that will never become reality. > > So, when you fix the bug that always supress the warnings, you will at the > same time cause a regression on those boxes, which will now print undesired > warnings. If the user has manually set nr_cpus or maxcpus, maybe it would > be best to not print any warnings or alternatively to downgrade them to > debug level?
While I appreciate your concerns, I fail to see how they are related.
First, please keep in mind that my patch does not alter the (more common) case with CONFIG_HOTPLUG_CPU=y in any way. For the (presumably less common) !HOTPLUG_CPU case, it adds a warning that is always issued in the HOTPLUG_CPU case.
Second, regarding your use case, I don't think it changes anything. So, let's say you have a board with 16 CPUs and a MADT that describes 1024 CPUs. You know that there can (physically) be at most 48 CPUs, so you boot with nr_cpus=48:
num_processors = 16 /* online CPUs at boot */ disabled_cpus = 992 /* 1008 - 16 */
This results in:
total_cpus = 1008 /* this is purely informative, it is *NOT* used to size anything */ possible = 48 /* clamped to nr_cpu_ids */
A warning message (with or without my patch): 1024 Processors exceeds NR_CPUS limit of 48
Informative message: Allowing 16 CPUs, 32 hotplug CPUs
No other warning (with or without my patch).
Petr Tesarik SUSE L3 Team 1
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