LWN: Comments on "RCU: The Bloatwatch Edition"

RCU and patents

PaulMcKenney — Sun, 29 Mar 2009 20:23:51 +0000

My understanding is that you are free to use technology derived from IBM's RCU contributions in GPL-licensed free-software projects that use either GPLv2 or later. The most prominent special case of this is of course the Linux kernel.

Obligatory disclaimer: The above is my personal opinion. In particular, I am not a lawyer, nor do I play one on TV.

RCU: The Bloatwatch Edition

rafdz — Sat, 28 Mar 2009 19:24:39 +0000

Excuse my ignorance. I am somwehat reluctant to learn about RCU technology for the reason that i do not know what exactly is covered by patents and what is not covered. Does anyone know which RCU things are covered by patents and what are the implications of implementing some RCU technology in own proprietary or free code.

RCU: The Bloatwatch Edition

PaulMcKenney — Thu, 19 Mar 2009 16:01:11 +0000

Good catch!!! I need to use "+" or "|" in place of the "||". Or did you have something else in mind?

I checked rcuclassic.c and rcutree.c, and they avoid this problem because they simply call rcu_qsctr_inc() and rcu_bh_qsctr_inc() in sequence.

RCU: The Bloatwatch Edition

kraai — Thu, 19 Mar 2009 03:02:47 +0000

If rcu_qsctr_help(&rcu_ctrlblk) returns 1 when called by rcu_qsctr_inc, rcu_qsctr_help(&rcp_bh_ctrlblk) won't be called and, as a result, if rcu_bh_ctrlblk.donetail != rcu_bh_ctrlblk.curtail, rcu_bh_ctrlblk.donetail won't be updated. Would this cause the bottom-half callbacks to be unnecessarily delayed?