linux-kernel - Re: [PATCH v7 16/46] virtio

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Message-ID: <20141201114645.GA17505@redhat.com>
Date:	Mon, 1 Dec 2014 13:46:45 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	rusty@....ibm.com, nab@...ux-iscsi.org, pbonzini@...hat.com,
	thuth@...ux.vnet.ibm.com, Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v7 16/46] virtio_blk: v1.0 support

On Mon, Dec 01, 2014 at 12:33:15PM +0100, Cornelia Huck wrote:
> On Mon, 1 Dec 2014 11:26:58 +0200
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > For some places on data path, it might be worth it
> > to cache the correct value e.g. as part of device
> > structure. This replaces a branch with a memory load,
> > so the gain would have to be measured, best done
> > separately?
> 
> I think we'll want to do some measuring once the basic structure is
> in place anyway.

What's meant by in place here?

> We should make sure that e.g. s390 only takes minor
> hit due to all that swapping that is needed for standard-compliant
> devices. Caching the value might certainly help in some paths.

Well, this is queued in linux-next for 3.19, so
now's the time to do it :)
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