From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>,
Stephen Hemminger <stephen@networkplumber.org>,
dev@dpdk.org, qemu-devel@nongnu.org, "Wang,
Zhihong" <zhihong.wang@intel.com>
Subject: Re: [dpdk-dev] [Qemu-devel] [PATCH 1/2] vhost: enable any layout feature
Date: Mon, 10 Oct 2016 11:59:10 +0800 [thread overview]
Message-ID: <20161010035910.GY1597@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <20161010064113-mutt-send-email-mst@kernel.org>
On Mon, Oct 10, 2016 at 06:46:44AM +0300, Michael S. Tsirkin wrote:
> On Mon, Oct 10, 2016 at 11:37:44AM +0800, Yuanhan Liu wrote:
> > On Thu, Sep 29, 2016 at 11:21:48PM +0300, Michael S. Tsirkin wrote:
> > > On Thu, Sep 29, 2016 at 10:05:22PM +0200, Maxime Coquelin wrote:
> > > >
> > > >
> > > > On 09/29/2016 07:57 PM, Michael S. Tsirkin wrote:
> > > Yes but two points.
> > >
> > > 1. why is this memset expensive?
> >
> > I don't have the exact answer, but just some rough thoughts:
> >
> > It's an external clib function: there is a call stack and the
> > IP register will bounch back and forth.
>
> for memset 0? gcc 5.3.1 on fedora happily inlines it.
Good to know!
> > overkill to use that for resetting 14 bytes structure.
> >
> > Some trick like
> > *(struct virtio_net_hdr *)hdr = {0, };
> >
> > Or even
> > hdr->xxx = 0;
> > hdr->yyy = 0;
> >
> > should behaviour better.
> >
> > There was an example: the vhost enqueue optmization patchset from
> > Zhihong [0] uses memset, and it introduces more than 15% drop (IIRC)
> > on my Ivybridge server: it has no such issue on his server though.
> >
> > [0]: http://dpdk.org/ml/archives/dev/2016-August/045272.html
> >
> > --yliu
>
> I'd say that's weird. what's your config? any chance you
> are using an old compiler?
Not really, it's gcc 5.3.1. Maybe Zhihong could explain more. IIRC,
he said the memset is not well optimized for Ivybridge server.
--yliu
next prev parent reply other threads:[~2016-10-10 3:58 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 6:40 [dpdk-dev] [PATCH 0/2] enables vhost/virtio " Yuanhan Liu
2016-09-26 6:40 ` [dpdk-dev] [PATCH 1/2] vhost: enable " Yuanhan Liu
2016-09-26 18:01 ` Stephen Hemminger
2016-09-26 19:24 ` Michael S. Tsirkin
2016-09-27 3:11 ` Yuanhan Liu
2016-09-27 19:48 ` Stephen Hemminger
2016-09-27 19:56 ` Michael S. Tsirkin
2016-09-28 2:28 ` Yuanhan Liu
2016-09-29 15:30 ` [dpdk-dev] [Qemu-devel] " Maxime Coquelin
2016-09-29 17:57 ` Michael S. Tsirkin
2016-09-29 20:05 ` Maxime Coquelin
2016-09-29 20:21 ` Michael S. Tsirkin
2016-09-29 21:23 ` Maxime Coquelin
2016-09-30 12:05 ` Maxime Coquelin
2016-09-30 19:16 ` Michael S. Tsirkin
2016-10-10 4:05 ` Yuanhan Liu
2016-10-10 4:17 ` Michael S. Tsirkin
2016-10-10 4:22 ` Yuanhan Liu
2016-10-10 4:25 ` Michael S. Tsirkin
2016-10-10 12:40 ` Maxime Coquelin
2016-10-10 14:42 ` Yuanhan Liu
2016-10-10 14:54 ` Maxime Coquelin
2016-10-11 6:04 ` Yuanhan Liu
2016-10-11 6:39 ` Maxime Coquelin
2016-10-11 6:49 ` Yuanhan Liu
2016-10-03 14:20 ` Maxime Coquelin
2016-10-10 3:37 ` Yuanhan Liu
2016-10-10 3:46 ` Michael S. Tsirkin
2016-10-10 3:59 ` Yuanhan Liu [this message]
2016-10-10 4:16 ` Wang, Zhihong
2016-10-10 4:24 ` Michael S. Tsirkin
2016-10-10 4:39 ` Michael S. Tsirkin
2016-10-11 6:57 ` Yuanhan Liu
2016-10-12 3:21 ` Yuanhan Liu
[not found] ` <F5DF4F0E3AFEF648ADC1C3C33AD4DBF16C2409EB@SHSMSX101.ccr.corp.intel.com>
2016-10-13 2:52 ` Yang, Zhiyong
2016-10-10 3:50 ` Yuanhan Liu
2016-10-09 23:20 ` [dpdk-dev] " Michael S. Tsirkin
2016-10-10 3:03 ` Yuanhan Liu
2016-10-10 3:04 ` Michael S. Tsirkin
2016-10-10 3:10 ` Yuanhan Liu
2016-09-26 6:40 ` [dpdk-dev] [PATCH 2/2] net/virtio: " Yuanhan Liu
2016-09-26 18:04 ` Stephen Hemminger
2016-09-29 18:00 ` Michael S. Tsirkin
2016-09-29 18:01 ` Michael S. Tsirkin
2016-11-10 15:18 ` [dpdk-dev] [PATCH 0/2] enables vhost/virtio " Michael S. Tsirkin
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