From: Peter Zijlstra <peterz@infradead.org>
To: Florian Westphal <fw@strlen.de>
Cc: Anatol Pomozov <anatol.pomozov@gmail.com>,
Dmitry Vyukov <dvyukov@google.com>,
paulmck@linux.ibm.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: seqcount usage in xt_replace_table()
Date: Thu, 10 Jan 2019 21:25:33 +0100 [thread overview]
Message-ID: <20190110202533.GK2861@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20190110144812.mkbokbj2iyryj6lv@breakpoint.cc>
On Thu, Jan 10, 2019 at 03:48:12PM +0100, Florian Westphal wrote:
> Peter Zijlstra <peterz@infradead.org> wrote:
> > Is performance a concern in this path? There is no comment justifying
> > this 'creative' stuff.
>
> We have to wait until all cpus are done with current iptables ruleset.
>
> Before this 'creative' change, this relied on get_counters
> synchronization. And that caused wait times of 30 seconds or more on
> busy systems.
>
> I have no objections swapping this with a synchronize_rcu() if that
> makes it easier.
Would using synchronize_rcu() not also mean you can get rid of that
xt_write_recseq*() stuff entirely?
Anyway, synchronize_rcu() can also take a little while, but I don't
think anywere near 30 seconds.
> (synchronize_rcu might be confusing though, as we don't use rcu
> for table->private), and one 'has to know' that all the netfilter
> hooks, including the iptables eval loop, run with rcu_read_lock
> held).
A comment can help there, right?
next prev parent reply other threads:[~2019-01-10 20:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-08 19:33 seqcount usage in xt_replace_table() Anatol Pomozov
2019-01-08 22:37 ` Florian Westphal
2019-01-10 12:41 ` Peter Zijlstra
2019-01-10 12:53 ` Dmitry Vyukov
2019-01-10 20:18 ` Peter Zijlstra
2019-01-10 14:48 ` Florian Westphal
2019-01-10 20:20 ` Peter Zijlstra
2019-01-10 20:25 ` Peter Zijlstra [this message]
2019-01-10 22:29 ` Florian Westphal
2019-01-11 8:34 ` Peter Zijlstra
2019-01-11 14:08 ` Paul E. McKenney
2019-01-10 14:52 ` Paul E. McKenney
2019-01-09 0:02 ` Andrea Parri
2019-01-09 0:36 ` Anatol Pomozov
2019-01-09 5:35 ` Dmitry Vyukov
2019-01-09 11:24 ` Andrea Parri
2019-01-09 11:55 ` Dmitry Vyukov
2019-01-09 12:11 ` Andrea Parri
2019-01-09 12:29 ` Dmitry Vyukov
2019-01-09 17:10 ` Paul E. McKenney
2019-01-10 8:49 ` Dmitry Vyukov
2019-01-10 12:30 ` Andrea Parri
2019-01-10 12:38 ` Dmitry Vyukov
2019-01-10 12:46 ` Andrea Parri
2019-01-10 13:25 ` Dmitry Vyukov
2019-01-10 14:50 ` Paul E. McKenney
2019-01-10 12:44 ` Peter Zijlstra
2019-01-10 12:54 ` Dmitry Vyukov
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