lkml.org 
[lkml]   [2020]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subject[PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support
Date
Hi,

Changelog-v2
============

- Standardize on seqcount_LOCKNAME_t as the canonical reference for
sequence counters with associated locks, instead of v1
seqcount_LOCKTYPE_t.

- Use unique prefix "seqprop_*" for all seqcount_t/seqcount_LOCKNAME_t
property accessors.

- Touch-up the lock-unlock rationale for more clarity. Enforce writer
non-preemitiblity using "__seq_enforce_writer_non_preemptibility()".

Cover letter (v1)
=================

https://lkml.kernel.org/r/20200828010710.5407-1-a.darwish@linutronix.de

Preemption must be disabled before entering a sequence counter write
side critical section. Otherwise the read side section can preempt the
write side section and spin for the entire scheduler tick. If that
reader belongs to a real-time scheduling class, it can spin forever and
the kernel will livelock.

Disabling preemption cannot be done for PREEMPT_RT though: it can lead
to higher latencies, and the write side sections will not be able to
acquire locks which become sleeping locks (e.g. spinlock_t).

To remain preemptible, while avoiding a possible livelock caused by the
reader preempting the writer, use a different technique: let the reader
detect if a seqcount_LOCKNAME_t writer is in progress. If that's the
case, acquire then release the associated LOCKNAME writer serialization
lock. This will allow any possibly-preempted writer to make progress
until the end of its writer serialization lock critical section.

Implement this lock-unlock technique for all seqcount_LOCKNAME_t with
an associated (PREEMPT_RT) sleeping lock, and for seqlock_t.

8<--------------

Ahmed S. Darwish (5):
seqlock: seqcount_LOCKNAME_t: Standardize naming convention
seqlock: Use unique prefix for seqcount_t property accessors
seqlock: seqcount_t: Implement all read APIs as statement expressions
seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support
seqlock: PREEMPT_RT: Do not starve seqlock_t writers

include/linux/seqlock.h | 281 ++++++++++++++++++++++++----------------
1 file changed, 167 insertions(+), 114 deletions(-)

base-commit: f75aef392f869018f78cfedf3c320a6b3fcfda6b
--
2.28.0

\
 
 \ /
  Last update: 2020-09-04 17:32    [W:0.126 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site