lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Sat, 12 Mar 2022 03:11:04 +0000 From: "Zhang, Qiang1" <qiang1.zhang@...el.com> To: Sebastian Andrzej Siewior <bigeasy@...utronix.de> CC: "paulmck@...nel.org" <paulmck@...nel.org>, "frederic@...nel.org" <frederic@...nel.org>, "urezki@...il.com" <urezki@...il.com>, "quic_neeraju@...cinc.com" <quic_neeraju@...cinc.com>, "josh@...htriplett.org" <josh@...htriplett.org>, "juri.lelli@...hat.com" <juri.lelli@...hat.com>, "rcu@...r.kernel.org" <rcu@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [PATCH v3] rcu: Only boost rcu reader tasks with lower priority than boost kthreads On 2022-03-11 10:22:26 [+0800], Zqiang wrote: > When RCU_BOOST is enabled, the boost kthreads will boosting readers > who are blocking a given grace period, if the current reader tasks ^ Period. > have a higher priority than boost kthreads(the boost kthreads priority > not always 1, if the kthread_prio is set), >>This confuses me: >>- Why does this matter In preempt-rt system, if the kthread_prio is not set, it prio is 1. the boost kthreads can preempt almost rt task, It will affect the real-time performance of some user rt tasks. In preempt-rt systems, in most scenarios, this kthread_prio will be configured. Thanks Zqiang >>- If it is not RT prio, what is then? Higher or lower? Afaik it is >> always >= 1. >>>If it is not RT prio, the sanitize_kthread_prio() will limit RT prio > boosting is useless, skip > current task and select next task to boosting, reduce the time for a > given grace period. >>So if the task, that is stuck in a rcu_read() section, has a higher >>priority than the boosting thread then boosting is futile. Understood. >> >>Please correct me if I'm wrong but this is intended for !SCHED_OTHER >>tasks since there shouldn't a be PI chain on boost_mtx so that its >>default RT priority is boosted above what has been configured. >>>Yes, you are right. If the boosting task which itself already boosted due to PI chain, >>>and Its priority may only be temporarily higher than boost kthreads, once that >>>PI boost is lifted the task may still be in a RCU section, but if we have been skipped it, >>>this task have been missed the opportunity to be boosted. >> >>You skip boosting tasks which are itself already boosted due to a PI >>chain. Once that PI boost is lifted the task may still be in a RCU >>section. But if I understand you right, your intention is skip boosting >>tasks with a higher priority and concentrate and those which are in >>need. This shouldn't make a difference unless the scheduler is able to >>move the rcu-boosted task to another CPU. >> >>>Yes, It make sense when the rcu-boosted kthreads and task which to be boosting >>>should run difference CPU . >>Am I right so far? If so this should be part of the commit message (the >>intention and the result). Also, please add that part with >>boost_exp_tasks. The comment above boost_mtx is now above >>boost_exp_tasks with a space so it looks (at least to me) like these two >>don't belong together. >>>Yes, I will add your description to the commit information. > Suggested-by: Uladzislau Rezki (Sony) <urezki@...il.com> > Signed-off-by: Zqiang <qiang1.zhang@...el.com> >Sebastian
Powered by blists - more mailing lists