netdev - RE: [PATCH V2,net-next, 1/2] hv

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Date:   Tue, 21 Jan 2020 13:56:54 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     David Miller <davem@...emloft.net>
CC:     "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V2,net-next, 1/2] hv_netvsc: Add XDP support



> -----Original Message-----
> From: linux-hyperv-owner@...r.kernel.org <linux-hyperv-
> owner@...r.kernel.org> On Behalf Of David Miller
> Sent: Tuesday, January 21, 2020 5:05 AM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: sashal@...nel.org; linux-hyperv@...r.kernel.org; netdev@...r.kernel.org;
> KY Srinivasan <kys@...rosoft.com>; Stephen Hemminger
> <sthemmin@...rosoft.com>; olaf@...fle.de; vkuznets
> <vkuznets@...hat.com>; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH V2,net-next, 1/2] hv_netvsc: Add XDP support
> 
> From: Haiyang Zhang <haiyangz@...rosoft.com>
> Date: Mon, 20 Jan 2020 14:22:36 -0800
> 
> > +u32 netvsc_run_xdp(struct net_device *ndev, struct netvsc_channel *nvchan,
> > +		   struct xdp_buff *xdp)
> > +{
> > +	struct page *page = NULL;
> > +	void *data = nvchan->rsc.data[0];
> > +	u32 len = nvchan->rsc.len[0];
> > +	struct bpf_prog *prog;
> > +	u32 act = XDP_PASS;
> 
> Please use reverse christmas tree ordering of local variables.
> 
> > +	xdp->data_hard_start = page_address(page);
> > +	xdp->data = xdp->data_hard_start + NETVSC_XDP_HDRM;
> > +	xdp_set_data_meta_invalid(xdp);
> > +	xdp->data_end = xdp->data + len;
> > +	xdp->rxq = &nvchan->xdp_rxq;
> > +	xdp->handle = 0;
> > +
> > +	memcpy(xdp->data, data, len);
> 
> Why can't the program run directly on nvchan->rsc.data[0]?
> 
> This data copy defeats the whole performance gain of using XDP.

Sure I will update this, and the var order.

Thanks
- Haiyang