From: "Paul E. McKenney" <paulmck@us.ibm.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [DOCUMENTATION] Revised Unreliable Kernel Locking Guide
Date: Fri, 12 Dec 2003 11:35:59 -0800 [thread overview]
Message-ID: <20031212193559.GA1614@us.ibm.com> (raw)
In-Reply-To: <20031212052812.E80972C085@lists.samba.org>
On Fri, Dec 12, 2003 at 04:24:18PM +1100, Rusty Russell wrote:
> OK, I've put the html version up for your reading pleasure: the diff
> is quite extensive and hard to read.
>
> http://www.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/
>
> Feedback welcome,
> Rusty.
> --
> Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
Hello, Rusty,
Good stuff! A few comments, as always!
Thanx, Paul
Glossary:
o Hardware Interrupt / Hardware IRQ: How does in_irq()
know that interrupts have been blocked? The local_irq_disable()
does not seem to mess with the counter, and preempt_disable()
just does the standard inc/dec stuff...
o in_irq() is hardirq_count().
o hardirq_count() is (preempt_count() & HARDIRQ_MASK).
o preempt_count is an integer, HARDIRQ_MASK is a constant that
is out of the normal inc/dec range.
I see how an interrupt handler causes in_irq() to do its thing
via the irq_enter() and irq_exit() macros, but I don't see how
masking interrupts makes this happen.
Probably just my confusion, but...
Ditto for "in_interrupt()". That would be for both the
analysis and the probable confusion on my part.
o Software Interrupt / softirq: formatting botch "of'software".
This would be "o'software", right?
o Preemption: Would it be worth changing the first bit
of the second sentence to read something like: "In 2.5.4
and later, when CONFIG_PREEMPT is set, this changes:"?
Overzealous Prevention Of Deadlocks: Cute!!!
Avoiding Locks: Read Copy Update
o Might be worth noting explicitly early on that updaters are
running concurrently with readers. Should be obvious given
that the readers aren't doing any explicit synchronization,
but I have run into confusion on this point surprisingly often.
o Please add a note to the list_for_each_entry_rcu() description
saying that writers (who hold appropriate locks) need not use
the _rcu() variant.
o Don't understand the blank line before and after the
"struct rcu_head rcu;", but clearly doesn't affect
functionality. ;-)
o If nothing blocks between the call to __cache_find() and the
eventual object_put(), it is worthwhile to avoid the
reference-count manipulation. This would make all of
cache_find() be almost as fast as UP, rather than just
__cache_find().
next prev parent reply other threads:[~2003-12-13 2:40 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-12-12 5:24 [DOCUMENTATION] Revised Unreliable Kernel Locking Guide Rusty Russell
2003-12-12 15:44 ` Dave Jones
2003-12-12 16:25 ` Keith Owens
2003-12-12 18:25 ` Dave Jones
2003-12-13 0:28 ` Keith Owens
2003-12-12 21:05 ` Rob Love
2003-12-15 2:28 ` Rusty Russell
2003-12-12 19:35 ` Paul E. McKenney [this message]
2003-12-13 3:16 ` Zwane Mwaikambo
2003-12-15 5:17 ` Rusty Russell
2003-12-15 5:17 ` Rusty Russell
2003-12-15 22:22 ` Paul E. McKenney
2003-12-16 6:32 ` Rusty Russell
2003-12-13 3:15 Manfred Spraul
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