Re: [patch 00/63] locking, sched: The PREEMPT-RT locking infrastructure

From: Daniel Bristot de Oliveira
Date: Tue Aug 03 2021 - 08:38:05 EST


On 7/30/21 3:50 PM, Thomas Gleixner wrote:
> Folks,
>
> the following series is an update to V1 which can be found here:
>
> https://lore.kernel.org/r/20210713151054.700719949@xxxxxxxxxxxxx
>
> It contains the bulk of the PREEMPT-RT locking infrastructure. In
> PREEMPT-RT enabled kernels the following locking primitives are substituted
> by RT-Mutex based variants:
>
> mutex, rw_semaphore, spinlock, rwlock
>
> semaphores are not substituted because they do not provide strict owner
> semantics.
>
> ww_mutexes are also not substituted because the usage sites are not really
> RT relevant and it would require a full reimplementation to make them work
> correctly based on rtmutex. That might change in the future, but for now
> utilizing the existing variant is considered a safe and sane choice.
>
> Of course raw_spinlocks are not touched either as they protect low level
> operations in the scheduler, timers and hardware access.
>
> The most interesting parts of the series which need a lot of eyeballs
> are:
>
> - the scheduler bits which provide the infrastructure for spinlock and
> rwlock substitution to ensure that the task state is preserved when
> blocking on such a lock and a regular wakeup is handled correctly and
> not lost
>
> - the rtmutex core implementation to handle lock contention on spinlocks
> and rwlocks correctly vs. the task state
>
> - the rw_semaphore/rwlock substitutions which utilize the same
> implementation vs. the reader/writer handling
>
> - the isolation of the ww_mutex code which allows to build it stand alone.
> The typedef based solution might look a bit odd on the first glance,
> but that turned out to be the least intrusive variant.
>
> - the PI futex related bits to handle the interaction between blocking
> on the underlying rtmutex and contention on the hash bucket lock which
> is converted to a 'sleeping spinlock'.
>
> The rest surely needs a thorough review as well, but those parts are pretty
> straight forward. Quite some code restructuring and the actual wrapper
> functions to replace the existing !RT implementations.
>
> The series survived quite some internal testing in RT kernels and is part
> of the recent 5.14-rc3-rt2 release.
>
> For !RT kernels there is no functional change.
>
> The series is also available from git:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rtmutex
>
> and fully integrated into the v5.14-rc3-rt2 release:
>
> https://lore.kernel.org/r/20210730131256.7d3jccmpuiw5pr4o@xxxxxxxxxxxxx

Thomas,

While reviewing/testing this series, I ended up finding some (simple) typos,
reporting them here:

patch 2:
unneccesary -> unnecessary

patches 2/3/27/29/31:
accross -> across

patch 4:
optimze -> optimize

patches 4/15:
seperately -> separately

patches 5(2x)/12/17/18:
seperate -> separate

patch 11:
appropiate -> appropriate

patch 15:
indentical -> identical

patch 34:
Preperatory -> Preparatory

patch 53:
completness -> completeness

patch 61:
Signficant -> Significant

continuing the testing...

-- Daniel