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readme: further interlink _NPROCESSORS_CONF and controlling the --cpus count

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Ciro Santilli 六四事件 法轮功
2019-11-11 00:00:00 +00:00
parent 4aff114c4c
commit 86caa918a8
1 changed files with 13 additions and 2 deletions
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README.adoc
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@@ -10650,13 +10650,24 @@ cat /proc/cpuinfo
getconf _NPROCESSORS_CONF
....
Or from <<user-mode-simulation>>, we can use <<sysconf>> with link:userland/linux/sysconf.c[] or <<cpp-multithreading>>'s link:userland/cpp/thread_hardware_concurrency.cpp[]:
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./run --cpus 2 --emulator gem5 --userland userland/linux/sysconf.c | grep _SC_NPROCESSORS_ONLN
./run --cpus 2 --emulator gem5 --userland userland/cpp/thread_hardware_concurrency.cpp
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====== QEMU user mode multithreading
TODO why in <<user-mode-simulation>> QEMU always shows the number of cores of the host. E.g., both of the following output the same as `nproc` on the host:
<<user-mode-simulation>> QEMU v4.0.0 always shows the number of cores of the host, presumably because the thread switching uses host threads directly which would make that harder to implement.
It does not seem possible to make the guest see a different number of cores than what the host has. Full system does have the `-smp` options, which controls this.
E.g., all of of the following output the same as `nproc` on the host:
....
nproc
./run --userland userland/cpp/thread_hardware_concurrency.cpp
./run --cpus 1 --userland userland/cpp/thread_hardware_concurrency.cpp
./run --cpus 2 --userland userland/cpp/thread_hardware_concurrency.cpp
....