linux-kernel - [PATCH v2 0/5] rcu,nohz,kvm: use RCU extended quiescent state when running KVM guest

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Message-Id: <1423167832-17609-1-git-send-email-riel@redhat.com>
Date:	Thu,  5 Feb 2015 15:23:47 -0500
From:	riel@...hat.com
To:	kvm@...r.kernel.org
Cc:	borntraeger@...ibm.com, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com, mingo@...nel.orgm, ak@...ux.intel.com,
	oleg@...hat.com, masami.hiramatsu.pt@...achi.com,
	fweisbec@...il.com, paulmck@...ux.vnet.ibm.com,
	lcapitulino@...hat.com, pbonzini@...hat.com
Subject: [PATCH v2 0/5] rcu,nohz,kvm: use RCU extended quiescent state when running KVM guest

When running a KVM guest on a system with NOHZ_FULL enabled, and the
KVM guest running with idle=poll mode, we still get wakeups of the
rcuos/N threads.

This problem has already been solved for user space by telling the
RCU subsystem that the CPU is in an extended quiescent state while
running user space code.

This patch series extends that code a little bit to make it usable
to track KVM guest space, too.

I tested the code by booting a KVM guest with idle=poll, on a system
with NOHZ_FULL enabled on most CPUs, and a VCPU thread bound to a
CPU. In a 10 second interval, rcuos/N threads on other CPUs got woken
up several times, while the rcuos thread on the CPU running the bound
and alwasy running VCPU thread never got woken up once.

Thanks to Christian Borntraeger and Paul McKenney for reviewing the
first version of this patch series, and helping optimize patch 4/5.

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