From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCHv2/RFC] kvm/irqchip: Speed up KVM_SET_GSI_ROUTING
Date: Thu, 16 Jan 2014 13:59:14 +0100
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Cc: Gleb Natapov <gleb@minantech.com>, KVM <kvm@vger.kernel.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	Jens Freimann <jfrei@linux.vnet.ibm.com>, agraf@suse.de,
	mst@redhat.com
To: Christian Borntraeger <borntraeger@de.ibm.com>
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Il 16/01/2014 13:44, Christian Borntraeger ha scritto:
> I converted most of the rcu routines to srcu. Review for the unconverted
> use of hlist_for_each_entry_rcu, hlist_add_head_rcu, hlist_del_init_rcu
> is necessary, though. They look fine to me since they are protected by
> outer functions.

They are fine because they do not have lockdep checks
(hlist_for_each_entry_rcu uses rcu_dereference_raw rather than
rcu_dereference, and write-sides do not do rcu lockdep at all).

> In addition, we should also discuss if a global srcu (for all guests) is
> fine.

I think it is.  It is already way cheaper than it used to be, and we're
hardly relying on the "sleepable" part of srcu.  We just want its faster
detection of grace periods.  One instance should be fine because our
read sides are so small and mostly they are not even preemptable.

Thanks for writing the patch!

Paolo