scx_rustland: reduce overhead by caching host topology #238
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htejun
approved these changes
Apr 23, 2024
Byte-Lab
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Apr 24, 2024
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In case you want to give it a try, this might help: #241 |
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Introuce a TopologyMap object, represented as an array of arrays, where
each inner array corresponds to a core containing its associated CPU
IDs.
This object can be used as a cache to facilitate efficient iteration
over the entire host's topology.
Example usage:
let topo = Topology::new()?;
let topo_map = TopologyMap::new(topo)?;
for (core_id, core) in topo_map.iter().enumerate() {
for cpu in core {
println!("core={} cpu={}", core_id, cpu);
}
}
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Looking at perf top it seems that the scheduler can spend a significant amount of time iterating over the CPU topology/cpumask information, especially when the system is running a significant amount of tasks: 2.57% scx_rustland [.] <scx_utils::cpumask::CpumaskIntoIterator as core::iter::traits::iterator::Iterator>::next Considering that scx_rustland doesn't support CPU hotplugging yet (it requires a full restart to properly handle CPU hotplug events), we can completely avoid this overhead by caching a TopologyMap object at the beginning, when the scheduler starts, instead of constantly re-evaluating the CPU topology information. This allows to reduce the scheduler overhead by ~5% CPU utilization under heavy load conditions (from ~65% -> ~60%, according to top). Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
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(meh... pushed the wrong branch, should be good now) |
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Looking at
perf topit seems that the scheduler can spend a significant amount of time in topology::Cache::span(), especially when the system is running a significant amount of tasks:5.46% scx_rustland [.] scx_utils::topology::Cache::span
Considering that scx_rustland doesn't support CPU hotplugging yet (it requires a full restart to properly handle CPU hotplug events), we can completely avoid this overhead by caching the cores/CPUs mapping at the beginning, when the scheduler starts, instead of constantly re-evaluating the CPU topology information.
This allows to reduce the scheduler overhead by ~10% CPU utilization under heavy load conditions (from ~68% -> ~60%, according to
top).