From mboxrd@z Thu Jan  1 00:00:00 1970
From: cohuck@redhat.com (Cornelia Huck)
Date: Tue, 29 Aug 2017 13:23:42 +0200
Subject: [PATCH RFC v3 1/9] KVM: s390: optimize detection of started vcpus
In-Reply-To: <67a8b09c-3e7a-943d-8684-f9ad6e70514b@redhat.com>
References: <20170821203530.9266-1-rkrcmar@redhat.com>
 <20170821203530.9266-2-rkrcmar@redhat.com>
 <67a8b09c-3e7a-943d-8684-f9ad6e70514b@redhat.com>
Message-ID: <20170829132342.1ef25500.cohuck@redhat.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, 22 Aug 2017 13:31:27 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 21.08.2017 22:35, Radim Kr?m?? wrote:
> > We can add a variable instead of scanning all online VCPUs to know how
> > many are started.  We can't trivially tell which VCPU is the last one,
> > though.  
> 
> You could keep the started vcpus in a list. Then you might drop unsigned
> started_vcpus;
> 
> No started vcpus: Start pointer NULL
> Single started vcpu: Only one element in the list (easy to check)
> > 1 started vcpus: More than one element int he list (easy to check)  

I'm not sure the added complication of keeping a list buys us much
here: We only have the "look for the last vcpu not stopped" operation
for the 2->1 transition.