Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] 2.5.21 Nonlinear CPU support | From | Robert Love <> | Date | 11 Jun 2002 10:59:25 -0700 |
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On Tue, 2002-06-11 at 03:57, Anton Altaparmakov wrote:
> This is crazy! It means you are allocating 2MiB of memory instead of just > 128kiB on a 2 CPU system, which will be about 99% of the SMP systems in > use, at my guess. So your change is throwing away 1920kiB of kernel ram for > no reason at all. And that is just ntfs... > > CPU hot plugging is an extremely specialised corner case so can you please > make it a config option and not get rid of smp_num_cpus? If people enable > the option make smp_num_cpus be the same as NR_CPUS and if not leave it be > as it is now.
I agree. One can argue these rants are just for "micro optimizations" (although I disagree the size issue is "micro") but someone has to stay on top of these issues...
Hot swappable CPUs is incredibly specialized and corner-cased.
> Anything else penalizes the majority of users just to allow a tiny minority > to do strange things like swap cpus without rebooting...
It is by no means a solution, but I just posted a patch to configure NR_CPUS... so setting it to, say, 2 on your dual box should help you out. On the converse, however, it introduces a default of 64 on 64-bit boxen so it compounds the problem for users who don't tweak the setting... something still needs to be done with the hotplug code.
Robert Love
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