From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>, Peter Anvin <hpa@zytor.com>,
Sasha Levin <sasha.levin@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jason Low <jason.low2@hp.com>,
Michel Lespinasse <walken@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Dave Jones <davej@codemonkey.org.uk>,
Ming Lei <ming.lei@canonical.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: [tip:locking/core] locking/rwsem: Fix lock optimistic spinning when owner is not running
Date: Tue, 10 Mar 2015 19:33:12 +0100 [thread overview]
Message-ID: <20150310183312.GA13665@redhat.com> (raw)
In-Reply-To: <CA+55aFwyfhSFk69nLAsqUy44vVAH+28g7U221L-JDdz1o9f2wA@mail.gmail.com>
On 03/10, Linus Torvalds wrote:
>
> So I'm not a huge fan of SLAB_DESTROY_BY_RCU in general, but for
> really core data structures like this, I think it's worth it.
I agree, but we have other users which can't be fixed if we just add
SLAB_DESTROY_BY_RCU to task_struct_cachep. So we need something else
anyway.
> The
> overhead of "call_rcu()" can be quite noticeable,
Yes, this was my concern too,
> and the other
> alternative solutions (like that suggested task_rcu_dereference()) are
> even *more* complex and subtle
Yes, but at least the ugliness is hidden inside task_rcu_dereference().
The usage is simple.
> and generally perform worse.
Well, task_rcu_dereference() should be cheap enough. probe_slab_address()
is a plain LOAD unless CONFIG_DEBUG_PAGEALLOC.
But!
> I'm not claiming it's perfect,
Same here, it is not that I think task_rcu_dereference() is very nice.
So I leave this to you and Peter ;)
Oleg.
next prev parent reply other threads:[~2015-03-10 18:35 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-07 7:45 [PATCH] locking/rwsem: Fix lock optimistic spinning when owner is not running Jason Low
2015-03-07 9:21 ` Peter Zijlstra
2015-03-09 17:42 ` Jason Low
2015-03-07 16:43 ` [tip:locking/core] " tip-bot for Jason Low
2015-03-07 17:13 ` Oleg Nesterov
2015-03-10 10:59 ` Peter Zijlstra
2015-03-10 16:04 ` Linus Torvalds
2015-03-10 16:16 ` Peter Zijlstra
2015-03-10 17:28 ` Oleg Nesterov
2015-03-10 17:45 ` Linus Torvalds
2015-03-10 18:33 ` Oleg Nesterov [this message]
2015-03-07 18:17 ` [PATCH] " Sasha Levin
2015-03-09 17:37 ` Jason Low
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