Date: Tue, 2 Apr 2019 21:02:53 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> Cc: musl <musl@...ts.openwall.com>, Michael Jeanson <mjeanson@...icios.com>, Richard Purdie <richard.purdie@...uxfoundation.org>, Jonathan Rajotte <jonathan.rajotte-julien@...icios.com> Subject: Re: sysconf(_SC_NPROCESSORS_CONF) returns the wrong value * Mathieu Desnoyers <mathieu.desnoyers@...icios.com> [2019-03-26 14:01:08 -0400]: > ----- On Mar 26, 2019, at 1:45 PM, Szabolcs Nagy nsz@...t70.net wrote: > > i agree that the current behaviour is not ideal, but > > iterating over /sys/devices/system/cpu/cpu* may not > > be correct either.. based on current linux api docs. > > > > i don't understand why is that number different from the > > cpu set in /sys/devices/system/cpu/possible > > I suspect both iteration over /sys/devices/system/cpu/cpu* and > content of /sys/devices/system/cpu/possible should provide the > same result. However, looking at Linux > Documentation/ABI/testing/sysfs-devices-system-cpu , > it appears that /sys/devices/system/cpu/possible was introduced > in December 2008, whereas /sys/devices/system/cpu/cpu#/ was there > pre-git history. > > This could explain why glibc uses the iteration method. > > Thoughts ? as far as i can tell the cpu iteration method is valid, and that directory list cannot change after boot (is this guaranteed by the linux abi in the future?), so as long as /sys is mounted we can get the number, but it's fairly ugly.. does lttng have fallback code if sysconf returns -1? if it does maybe musl should just do that (or somebody has to write cancellation safe directory traversal code)
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