From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
"Sebastian A. Siewior" <bigeasy@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>
Subject: [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support
Date: Fri, 4 Sep 2020 17:32:26 +0200 [thread overview]
Message-ID: <20200904153231.11994-1-a.darwish@linutronix.de> (raw)
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
next reply other threads:[~2020-09-04 15:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 15:32 Ahmed S. Darwish [this message]
2020-09-04 15:32 ` [PATCH v2 1/5] seqlock: seqcount_LOCKNAME_t: Standardize naming convention Ahmed S. Darwish
2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 2/5] seqlock: Use unique prefix for seqcount_t property accessors Ahmed S. Darwish
2020-09-08 11:41 ` peterz
2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 3/5] seqlock: seqcount_t: Implement all read APIs as statement expressions Ahmed S. Darwish
2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 4/5] seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support Ahmed S. Darwish
2020-09-08 11:45 ` peterz
2020-09-08 12:48 ` Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 5/5] seqlock: PREEMPT_RT: Do not starve seqlock_t writers Ahmed S. Darwish
2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-15 0:20 ` [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support Qian Cai
2020-09-15 12:48 ` Boqun Feng
2020-09-15 13:10 ` Boqun Feng
2020-09-15 14:30 ` peterz
2020-09-16 12:52 ` Qian Cai
2020-09-16 12:54 ` peterz
2020-09-16 13:00 ` Qian Cai
2020-09-16 13:02 ` peterz
2020-09-17 2:31 ` Stephen Rothwell
2020-09-18 8:42 ` [tip: locking/core] seqlock: Unbreak lockdep tip-bot2 for peterz@infradead.org
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200904153231.11994-1-a.darwish@linutronix.de \
--to=a.darwish@linutronix.de \
--cc=bigeasy@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).