From: David Woodhouse <dwmw2@infradead.org>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
paulmck@linux.vnet.ibm.com
Cc: peterz@infradead.org, mhillenb@amazon.de,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode
Date: Thu, 12 Jul 2018 12:10:28 +0100 [thread overview]
Message-ID: <1531393828.8759.116.camel@infradead.org> (raw)
In-Reply-To: <b3c188f7-454f-35da-b9aa-ddddc4d494cc@de.ibm.com>
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On Thu, 2018-07-12 at 13:00 +0200, Christian Borntraeger wrote:
>
> On s390 this seems to add about 10ns (~3%) for a guest exit/rentry
> microbenchmark mostly due to rcu_eqs_enter and rcu_eqs_exit now being
> visible in perf samples. The older interface was cheaper.
Well, the older interface wasn't actually working, which made it
moderately suboptimal :)
But that is fixed by the first patch of the two, so perhaps the second
ought to be conditional on CONFIG_NO_HZ_FULL since it's only really
fixing a real bug there?
Unless we can contrive some way to do the rcu_eqs_enter/exit only on
the paths to/from userspace, and *not* when we loop in the kernel to
handle interrupts (etc.) and immediately re-enter the guest without
returning? That's somewhat non-trivial though...
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next prev parent reply other threads:[~2018-07-12 11:10 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180709163432.GV3593@linux.vnet.ibm.com>
[not found] ` <1531162254.26547.3.camel@infradead.org>
[not found] ` <20180709203441.GE3593@linux.vnet.ibm.com>
[not found] ` <1531168538.26547.5.camel@infradead.org>
[not found] ` <20180709204248.GF3593@linux.vnet.ibm.com>
[not found] ` <1531169145.26547.8.camel@infradead.org>
[not found] ` <20180709210532.GH3593@linux.vnet.ibm.com>
[not found] ` <20180709220823.GA18045@linux.vnet.ibm.com>
[not found] ` <1531319025.8759.57.camel@infradead.org>
[not found] ` <20180711144303.GQ3593@linux.vnet.ibm.com>
[not found] ` <20180711164952.GA29994@linux.vnet.ibm.com>
2018-07-11 17:03 ` [RFC] Make need_resched() return true when rcu_urgent_qs requested David Woodhouse
2018-07-11 17:48 ` Paul E. McKenney
2018-07-11 18:01 ` [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode David Woodhouse
2018-07-11 18:20 ` Paul E. McKenney
2018-07-11 18:36 ` Paul E. McKenney
2018-07-11 18:39 ` Christian Borntraeger
2018-07-11 20:27 ` Paul E. McKenney
2018-07-11 20:54 ` David Woodhouse
2018-07-11 21:09 ` Paul E. McKenney
2018-07-11 21:11 ` Christian Borntraeger
2018-07-11 21:32 ` Paul E. McKenney
2018-07-11 21:39 ` Christian Borntraeger
2018-07-11 23:47 ` Paul E. McKenney
2018-07-12 8:31 ` David Woodhouse
2018-07-12 11:00 ` Christian Borntraeger
2018-07-12 11:10 ` David Woodhouse [this message]
2018-07-12 11:58 ` Christian Borntraeger
2018-07-12 12:04 ` Christian Borntraeger
2018-07-11 23:37 ` Paul E. McKenney
2018-07-12 2:15 ` Paul E. McKenney
2018-07-12 6:21 ` Christian Borntraeger
2018-07-12 9:52 ` David Woodhouse
2018-07-11 18:31 ` [RFC] Make need_resched() return true when rcu_urgent_qs requested Christian Borntraeger
2018-07-11 20:17 ` Paul E. McKenney
2018-07-11 20:19 ` David Woodhouse
2018-07-11 21:08 ` Paul E. McKenney
2018-07-12 12:00 ` David Woodhouse
2018-07-12 12:53 ` Paul E. McKenney
2018-07-12 16:17 ` Paul E. McKenney
2018-07-16 15:40 ` Paul E. McKenney
2018-07-17 8:19 ` David Woodhouse
2018-07-17 12:56 ` Paul E. McKenney
2018-07-18 15:36 ` Paul E. McKenney
2018-07-18 16:01 ` David Woodhouse
2018-07-18 16:37 ` Paul E. McKenney
2018-07-18 19:41 ` David Woodhouse
2018-07-18 20:17 ` Paul E. McKenney
2018-07-19 0:26 ` Frederic Weisbecker
2018-07-19 6:45 ` Christian Borntraeger
2018-07-19 7:20 ` David Woodhouse
2018-07-19 10:23 ` Christian Borntraeger
2018-07-19 12:55 ` Paul E. McKenney
2018-07-19 13:14 ` Frederic Weisbecker
2018-07-19 13:36 ` David Woodhouse
2018-07-19 17:09 ` Paul E. McKenney
2018-07-23 8:08 ` David Woodhouse
2018-07-23 12:22 ` Paul E. McKenney
2018-07-19 0:32 ` Frederic Weisbecker
2018-07-19 3:11 ` Paul E. McKenney
2018-07-19 6:16 ` David Woodhouse
2018-07-19 13:17 ` Frederic Weisbecker
2018-07-19 13:15 ` Frederic Weisbecker
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