2011 Kernel Summit
, Google developer
Paul Turner described a scheduler testing framework which, he said, would
be released soon. Naturally, things took longer than expected, but, on
March 14, Paul released
a version of
Linsched for general use. Given the amount of interest in this tool, it's
likely that it will find its way into the mainline in a relative hurry.
Linsched is a framework that can run the kernel scheduler with various
simulated workloads and draw conclusions about the quality of the decisions
made. It looks at overall CPU utilization, the number of migrations, and
more. It is able to simulate a wide range of hardware topologies with
The original Linsched posting was quite intrusive; it inserted over 5,000
lines of code into the kernel behind "#ifdef LINSCHED" lines.
A determined effort has reduced that number slightly - to all of 20 lines
of code. The rest has been cleverly hidden in a special "linsched"
architecture that provides just enough support to run the scheduler in user
space. The actual simulation and measurement code lives in the
Making changes to the scheduler is a notoriously difficult task; one can
easily add regressions for specific workloads that go unnoticed until the
changes go into production. With enough simulated topologies and
workloads, a tool like Linsched should be able to remove a lot of that risk
from scheduler development. And that should lead to better kernel releases
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