From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [RFC PATCH V3 0/5] Hi:
Date: Sun, 6 Jan 2019 22:28:56 -0500
Message-ID: <20190106221832-mutt-send-email-mst@kernel.org>
References: <20181229124656.3900-1-jasowang@redhat.com>
 <20190102154038-mutt-send-email-mst@kernel.org>
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Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        davem@davemloft.net
To: Jason Wang <jasowang@redhat.com>
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On Mon, Jan 07, 2019 at 10:19:03AM +0800, Jason Wang wrote:
> 
> On 2019/1/3 上午4:47, Michael S. Tsirkin wrote:
> > On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:
> > > This series tries to access virtqueue metadata through kernel virtual
> > > address instead of copy_user() friends since they had too much
> > > overheads like checks, spec barriers or even hardware feature
> > > toggling.
> > Will review, thanks!
> > One questions that comes to mind is whether it's all about bypassing
> > stac/clac.  Could you please include a performance comparison with
> > nosmap?
> > 
> 
> On machine without SMAP (Sandy Bridge):
> 
> Before: 4.8Mpps
> 
> After: 5.2Mpps

OK so would you say it's really unsafe versus safe accesses?
Or would you say it's just a better written code?

> On machine with SMAP (Broadwell):
> 
> Before: 5.0Mpps
> 
> After: 6.1Mpps
> 
> No smap: 7.5Mpps
> 
> 
> Thanks


no smap being before or after?

-- 
MST