linux-kernel - RE: [PATCH net-next, v2, 1/3] hv_netvsc: Add support for LRO/RSC in the vSwitch

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Date:   Fri, 21 Sep 2018 18:51:54 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        vkuznets <vkuznets@...hat.com>
Subject: RE: [PATCH net-next, v2, 1/3] hv_netvsc: Add support for LRO/RSC in
 the vSwitch



> -----Original Message-----
> From: Stephen Hemminger <stephen@...workplumber.org>
> Sent: Friday, September 21, 2018 2:37 PM
> To: Haiyang Zhang <haiyangz@...uxonhyperv.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>; davem@...emloft.net;
> netdev@...r.kernel.org; olaf@...fle.de; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; vkuznets <vkuznets@...hat.com>
> Subject: Re: [PATCH net-next, v2, 1/3] hv_netvsc: Add support for LRO/RSC in
> the vSwitch
> 
> On Fri, 21 Sep 2018 18:20:35 +0000
> Haiyang Zhang <haiyangz@...uxonhyperv.com> wrote:
> 
> Overall, this looks good. Some minor suggestions.
> 
> > +struct nvsc_rsc {
> > +	const struct ndis_pkt_8021q_info *vlan;
> > +	const struct ndis_tcp_ip_checksum_info *csum_info;
> > +	u8 is_last; /* last RNDIS msg in a vmtransfer_page */
> > +	u32 cnt; /* #fragments in an RSC packet */
> > +	u32 pktlen; /* Full packet length */
> > +	void *data[NVSP_RSC_MAX];
> > +	u32 len[NVSP_RSC_MAX];
> > +};
> > +
> 
> This new state structure is state on a per-channel basis.
> Do you really need this to be persistent across packets?
> 
> Could this be on stack or do you need it to handle split packets arriving in
> different polls? Or is the stack space a problem?
> 
> Also, maybe data and length could be in one structure since they are related.

The stack space is a problem. NVSP_RSC_MAX is 562, which is defined by host.
It will be too large for limited stack space. 

struct nvsc_rsc includes the data, len, cnt, chksum, vlan for one RSC packet. They
are all related to construction of one SKB and its meta data. So I put them in
one structure.

Thanks,
- Haiyang