mirror of
https://github.com/xen-project/xen.git
synced 2026-10-28 10:11:27 +01:00
George Dunlap
58feb9e0ac
The credit scheduler tries as hard as it can to ensure that it always runs scheduling units with positive credit (PRI_TS_UNDER) before running those with negative credit (PRI_TS_OVER). If the next runnable scheduling unit is of priority OVER, it will always run the load balancer, which will scour the system looking for another scheduling unit of the UNDER priority. Unfortunately, as the number of cores on a system has grown, the cost of the work-stealing algorithm has dramatically increased; a recent trace on a system with 128 cores showed this taking over 50 microseconds. Add a parameter, load_balance_ratelimit, to limit the frequency of load balance operations on a given pcpu. Default this to 1 millisecond. Invert the load balancing conditional to make it more clear, and line up more closely with the comment above it. Overall it might be cleaner to have the last_load_balance checking happen inside csched_load_balance(), but that would require either passing both now and spc into the function, or looking them up again; both of which seemed to be worse than simply checking and setting the values before calling it. On a system with a vcpu:pcpu ratio of 2:1, running Windows guests (which will end up calling YIELD during spinlock contention), this patch increased performance significantly. Signed-off-by: George Dunlap <george.dunlap@cloud.com> Reviewed-by: Juergen Gross <jgross@suse.com> Release-acked-by: Henry Wang <Henry.Wang@arm.com>
Sphinx documentation:
All source rendered by Sphinx is licensed under CC-BY-4.0.
You are free to:
Share:
Copy and redistribute the material in any medium or format.
Adapt:
Remix, transform, and build upon the material for any purpose, even
commercially.
Under the following terms:
Attribution:
You must give appropriate credit, provide a link to the license, and
indicate if changes were made. You may do so in any reasonable manner, but
not in any way that suggests the licensor endorses you or your use.
No additional restrictions:
You may not apply legal terms or technological measures that legally
restrict others from doing anything the license permits.
See https://creativecommons.org/licenses/by/4.0/ for full details.
This includes:
* All ReStructured Text files: docs/*/*.rst
* The Sphinx configuration file: docs/conf.py
* Content in Sphinx-exclusive subdirs: docs/*-guide/*
Other documentation:
There are a variety of text documents in various formats. These, given no
explicit license guidance, fall under Xen's default GPL-2.0 license.