From: Randy Dunlap <rdunlap@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/9] Documentation: Add lock ordering and nesting documentation
Date: Mon, 16 Mar 2020 08:13:38 -0700 [thread overview]
Message-ID: <de6fdc5d-690a-1130-c911-caccbb0b1a8f@infradead.org> (raw)
In-Reply-To: <20200316103454.iodi65uzbpat4kv5@linutronix.de>
On 3/16/20 3:34 AM, Sebastian Andrzej Siewior wrote:
> On 2020-03-14 15:57:24 [-0700], Randy Dunlap wrote:
>> Hi,
> Hi Randy,
>
>> A few comments for your consideration:
>
> I merged all of you comments but two:
>
>> On 3/13/20 10:46 AM, Sebastian Andrzej Siewior wrote:
> …
>>> +rwlock_t and PREEMPT_RT
>>> +-----------------------
>>> +
>>> +On a PREEMPT_RT enabled kernel rwlock_t is mapped to a separate
>>> +implementation based on rt_mutex which changes the semantics:
>>> +
>>> + - Same changes as for spinlock_t
>>> +
>>> + - The implementation is not fair and can cause writer starvation under
>>> + certain circumstances. The reason for this is that a writer cannot
>>> + inherit its priority to multiple readers. Readers which are blocked
>>
>> ^^^^^^^ I think this is backwards. Maybe more like so:
>> a writer cannot
>> bequeath or grant or bestow or pass down ... its priority to
>
> So the term "inherit" is the problem. The protocol is officially called
> PI which is short for Priority Inheritance. Other documentation,
> RT-mutex for instance, is also using this term when it is referring to
> altering the priority of a task. For that reason I prefer to keep using
> this term.
OK, I get it.
>>> + on a writer fully support the priority inheritance protocol.
> …
>>> +raw_spinlock_t
>>> +--------------
>>> +
>>> +As raw_spinlock_t locking disables preemption and eventually interrupts the
>>> +code inside the critical region has to be careful to avoid calls into code
>>
>> Can I buy a comma in there somewhere, please?
>> I don't get it as is.
>
> What about
>
> | As raw_spinlock_t locking disables preemption, and eventually interrupts, the
> | code inside the critical region has to be careful to avoid calls into code
>
> any better?
Yes.
thanks.
--
~Randy
next prev parent reply other threads:[~2020-03-16 15:13 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-13 17:46 [PATCH 0/9] Lock ordering documentation and annotation for lockdep Sebastian Andrzej Siewior
2020-03-13 17:46 ` [PATCH 1/9] Documentation: Add lock ordering and nesting documentation Sebastian Andrzej Siewior
2020-03-14 22:57 ` Randy Dunlap
2020-03-16 10:34 ` Sebastian Andrzej Siewior
2020-03-16 15:13 ` Randy Dunlap [this message]
2020-03-13 17:46 ` [PATCH 2/9] timekeeping: Split jiffies seqlock Sebastian Andrzej Siewior
2020-03-13 17:46 ` [PATCH 3/9] pci/switchtec: Don't abuse completion wait queue for poll Sebastian Andrzej Siewior
2020-03-13 18:11 ` Logan Gunthorpe
2020-03-14 0:23 ` Thomas Gleixner
2020-03-14 6:01 ` Logan Gunthorpe
2020-03-16 18:52 ` Thomas Gleixner
2020-03-16 19:24 ` Logan Gunthorpe
2020-03-16 19:34 ` Thomas Gleixner
2020-03-16 21:53 ` Logan Gunthorpe
2020-03-17 0:17 ` Thomas Gleixner
2020-03-17 1:15 ` Logan Gunthorpe
2020-03-13 19:31 ` Peter Zijlstra
2020-03-13 17:46 ` [PATCH 4/9] sched/swait: Prepare usage in completions Sebastian Andrzej Siewior
2020-03-14 0:26 ` Thomas Gleixner
2020-03-13 17:46 ` [PATCH 5/9] completion: Use simple wait queues Sebastian Andrzej Siewior
2020-03-14 15:40 ` Linus Torvalds
2020-03-16 18:55 ` Thomas Gleixner
2020-03-13 17:46 ` [PATCH 6/9] lockdep: Introduce wait-type checks Sebastian Andrzej Siewior
2020-03-31 13:25 ` Geert Uytterhoeven
2020-03-31 13:42 ` Sebastian Andrzej Siewior
2020-03-31 14:55 ` Peter Zijlstra
2020-03-31 15:28 ` Peter Zijlstra
2020-03-31 15:37 ` Frederic Weisbecker
2020-03-13 17:46 ` [PATCH 7/9] lockdep: Add hrtimer context tracing bits Sebastian Andrzej Siewior
2020-03-13 17:47 ` [PATCH 8/9] lockdep: Annotate irq_work Sebastian Andrzej Siewior
2020-03-13 17:47 ` [PATCH 9/9] lockdep: Add posixtimer context tracing bits Sebastian Andrzej Siewior
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=de6fdc5d-690a-1130-c911-caccbb0b1a8f@infradead.org \
--to=rdunlap@infradead.org \
--cc=bigeasy@linutronix.de \
--cc=joel@joelfernandes.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--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).