linux-kernel - Re: [PATCH v2 0/7] swait: Introduce and use swq_has

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Date:   Fri, 15 Sep 2017 13:53:15 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org,
        peterz@...radead.org
Cc:     npiggin@...il.com, paulmck@...ux.vnet.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH v2 0/7] swait: Introduce and use swq_has_sleeper()

On 13/09/2017 22:08, Davidlohr Bueso wrote:
> The following patches fix and/or justify (in baby steps) some of the
> callers. The main exception is s390, which I didn't follow how ->valid_wakeup
> can get hoisted as kvm_vcpu_block does not use that in the wait loop.

valid_wakeup is just an optimization, so it's not a problem.

There seems to be always an atomic_or or set_bit before
kvm_s390_vcpu_wakeup is called (except kvm_s390_idle_wakeup which has no
store at all and doesn't need any serialization).  So my suggestion is
to add an smp__mb_after_atomic in kvm_s390_vcpu_wakeup; I'll let the
s390 guys do it.

Paolo