linux-kernel - Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems

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Message-ID: <1380751112.645.64.camel@pasglop>
Date:	Thu, 03 Oct 2013 07:58:32 +1000
From:	Benjamin Herrenschmidt <benh@....ibm.com>
To:	Alexander Graf <agraf@...e.de>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Gleb Natapov <gleb@...hat.com>,
	Michael Ellerman <michael@...erman.id.au>,
	linux-kernel@...r.kernel.org, mpm@...enic.com,
	herbert@...dor.hengli.com.au, linuxppc-dev@...abs.org,
	kvm@...r.kernel.org, kvm-ppc@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on
 some powernv systems

On Wed, 2013-10-02 at 11:11 +0200, Alexander Graf wrote:

> Right, and the difference for the patch in question is really whether
> we handle in in kernel virtual mode or in QEMU, so the bulk of the
> overhead (kicking threads out of  guest context, switching MMU
> context, etc) happens either way.
> 
> So the additional overhead when handling it in QEMU here really boils
> down to the user space roundtrip (plus another random number read
> roundtrip).

Hrm, Michael had a real mode version ... not sure where it went then.

Cheers,
Ben.


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