Fix some things in Nest #39
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Julia pointed out that our current implementation of r_impatient is incorrect. r_impatient is meant to be a mechanism for more aggressively growing the primary nest if a task repeatedly isn't able to find a core. Right now, we trigger r_impatient if we're not able to find an attached or previous core in the primary nest, but we _should_ be triggering it only if we're unable to find _any_ core in the primary nest. Fixing the implementation to do this drastically decreases how aggressively we grow the primary nest when r_impatient is in effect. Reported-by: Julia Lawall <julia.lawall@inria.fr> Signed-off-by: David Vernet <void@manifault.com>
The core sched code calls select_task_rq() in a few places: the task wakeup path (typical path), the fork() path, and the exec() path. For nest scheduling, we don't want to select a core from the nest on the exec() path. If we were previously able to find an idle core, we would have found it on the fork() path, so we don't gain much by checking on the exec() path. In fact, it's actually harmful, because we could incorrectly blow up the primary nest unnecessarily by bumping the same task between multiple cores for no reason. Let's just opt-out of select_task_rq calls on the exec() path. Suggested-by: Julia Lawall <julia.lawall@inria.fr> Signed-off-by: David Vernet <void@manifault.com>
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The only feedback I can give: built, tested, appears to have no problems. |
htejun
approved these changes
Dec 18, 2023
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Julia noticed a few things that can be improved in scx_nest. Address them here