Messages in this thread | | | Date | Wed, 23 Nov 2011 15:52:43 -0500 | From | Jérôme Carretero <> | Subject | Q: Process creation and soft hot CPU affinity |
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Hi,
I noticed something this night. The process executions during a ./configure get spread among all the machine CPUs. When launching processes sequentially, why aren't they put to run on the same CPU ? I naively assume that the CPU has just finished its work and it's "hot". The others could continue resting in their C-states/P-states, or whatever.
To measure the performance impact of the current scheduling choices, I ran a little benchmark. I ran a time ./configure with/without cgroup CPU affinity and got significant difference.
benchmark_setup() { cgrp=1cpu ncpus=8 cgroup_mnt=/sys/fs/cgroup coreutils_tar=/var/paludis/distfiles/coreutils-8.13.tar.xz
mkdir -p $cgroup_mnt/$cgrp echo 0 > $cgroup_mnt/$cgrp/cpuset.mems echo $$ > $cgroup_mnt/$cgrp/tasks
cd /dev/shm }
benchmark() { tar xf $coreutils_tar
pushd coreutils* > /dev/null echo $* > $cgroup_mnt/$cgrp/cpuset.cpus echo 3 > /proc/sys/vm/drop_caches time sh ./configure > /dev/null popd > /dev/null
rm -rf coreutils* }
benchmark 0 benchmark $(cat $cgroup_mnt/cpuset.cpus)
Results:
with affinity to 1CPU: real 0m40.229s user 0m15.222s sys 0m9.409s
with affinity to all CPUs: real 1m20.832s user 0m31.089s sys 0m37.582s
Is there something that can be done ? I just want to start a discussion on this matter, perhaps I'll play with the scheduler if I get a few hints.
Regards,
-- cJ 3.2.0-rc2-Bidule-00400-g866d43c #1 SMP PREEMPT Tue Nov 22 13:51:00 EST 2011 x86_64
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