McKenney: Stupid RCU Tricks: Is RCU Watching?

[Posted May 27, 2022 by corbet]

Paul McKenney writes about why read-copy-update coverage is not universal in the kernel, the hazards that can result from that, and what is being done to improve the situation.

Unfortunately, an eternally watchful RCU is impractical in the Linux kernel due to energy-efficiency considerations. The problem is that if RCU watches an idle CPU, RCU needs that CPU to execute instructions. And making an idle CPU unnecessarily execute instructions (for a rather broad definition of the word “unnecessary”) will terminally annoy a great many people in the battery-powered embedded world. And for good reason: Making RCU avoid watching idle CPUs can provide 30-40% increases in battery lifetime.

Thanks!

Posted May 31, 2022 6:37 UTC (Tue) by oldtomas (guest, #72579) [Link] (1 responses)

Thanks for explaining this incredibly difficult stuff in a way that even me get the impression I could understand it.

This is what makes free software really free.

Re: Thanks!

Posted May 31, 2022 17:49 UTC (Tue) by PaulMcKenney (✭ supporter ✭, #9624) [Link]

Glad you liked it!