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Re: [PATCH] sysconf: Use conservative default for _SC_NPROCESSORS_ONLN [BZ #21542]


On 06/09/2017 02:17 PM, Zack Weinberg wrote:
> On Fri, Jun 9, 2017 at 8:11 AM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 06/02/2017 04:21 PM, Florian Weimer wrote:
>>> 2017-06-02  Florian Weimer  <fweimer@redhat.com>
>>>
>>>       [BZ #21542]
>>>       * sysdeps/unix/sysv/linux/getsysstats.c (__get_nprocs): Default to
>>>       two if no accurate information is available.
>>>       * posix/tst-sysconf-empty-chroot.c: New file.
>>>       * posix/Makefile (tests): Add it.
>>
>> Ping?
>>
>>   <https://sourceware.org/ml/libc-alpha/2017-06/msg00101.html>
> 
> It seems reasonable to me but I'm not sure I understand all of the implications.

The implication is that the Hotspot JVM no longer crashes in a chroot on
an SMP host because it assumes a UP host and elides atomics.

The downside is that some other application could choose to use
spinlocks on a UP system because glibc suggests it's SMP, which could
result in terrible performance.

All this is just for the corner case of an improperly setup
chroot/contain (lacking key parts of /sys and /proc).

Thanks,
Florian


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