From: Paolo Bonzini <pbonzini@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
kvm@vger.kernel.org
Subject: Re: [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock
Date: Thu, 31 Oct 2013 12:11:21 +0100 [thread overview]
Message-ID: <52723AD9.4040902@redhat.com> (raw)
In-Reply-To: <20131031064743.GB20205@redhat.com>
Il 31/10/2013 07:47, Gleb Natapov ha scritto:
> This looks dubious to me. All other smp_mb__after_* variants are there
> because some atomic operations have different memory barrier semantics on
> different arches,
It doesn't have to be arches; unlock APIs typically have release
semantics only, but SRCU is stronger.
> but srcu_read_unlock() have the same semantics on all
> arches, so smp_mb__after_srcu_read_unlock() becomes
> smp_mb__after_a_function_that_happens_to_have_mb_now_but_may_not_have_in_the_feature().
> How likely it is that smp_mb() will disappear from srcu_read_unlock()
> (if was added for a reason I guess)? May be we should change documentation
> to say that srcu_read_unlock() is a memory barrier which will reflect
> the reality.
That would be different from all other unlock APIs.
Paolo
next prev parent reply other threads:[~2013-10-31 11:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-30 19:09 [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock Michael S. Tsirkin
2013-10-30 20:15 ` Paul E. McKenney
2013-10-30 23:26 ` Michael S. Tsirkin
2013-10-31 4:56 ` Paul E. McKenney
2013-10-31 6:47 ` Gleb Natapov
2013-10-31 11:11 ` Paolo Bonzini [this message]
2013-10-31 12:28 ` Gleb Natapov
2013-10-31 13:57 ` Michael S. Tsirkin
2013-11-01 8:43 ` Paul E. McKenney
2013-10-31 11:14 ` Paolo Bonzini
2013-10-31 11:32 ` Michael S. Tsirkin
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