netdev - 答复: [vger.kernel.org代发]Re: [vger.kernel.org代发]Re: [PATCH net-next] net/ packet: fix TPACKET

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Message-ID: <de32975979434430b914de00916bee95@inspur.com>
Date:   Sat, 28 Mar 2020 08:36:12 +0000
From:   Yi Yang (杨燚)-云服务集团 
        <yangyi01@...pur.com>
To:     "willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>
CC:     "yang_y_yi@....com" <yang_y_yi@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "u9012063@...il.com" <u9012063@...il.com>
Subject: 答复: [vger.kernel.org代发]Re: [vger.kernel.org代发]Re: [PATCH net-next] net/ packet: fix TPACKET_V3 performance issue in case of TSO

-----邮件原件-----
发件人: Willem de Bruijn [mailto:willemdebruijn.kernel@...il.com] 
发送时间: 2020年3月27日 11:17
收件人: Yi Yang (杨燚)-云服务集团 <yangyi01@...pur.com>
抄送: willemdebruijn.kernel@...il.com; yang_y_yi@....com; netdev@...r.kernel.org; u9012063@...il.com
主题: Re: [vger.kernel.org代发]Re: [vger.kernel.org代发]Re: [PATCH net-next] net/ packet: fix TPACKET_V3 performance issue in case of TSO

> On Wed, Mar 25, 2020 at 8:45 PM Yi Yang (杨燚)-云服务集团 <yangyi01@...pur.com> wrote:
> >
> > By the way, even if we used hrtimer, it can't ensure so high performance improvement, the reason is every frame has different size, you can't know how many microseconds one frame will be available, early timer firing will be an unnecessary waste, late timer firing will reduce performance, so I still think the way this patch used is best so far.
> >
>
> The key differentiating feature of TPACKET_V3 is the use of blocks to efficiently pack packets and amortize wake ups.
>
> If you want immediate notification for every packet, why not just use TPACKET_V2?
>
> For non-TSO packet, TPACKET_V3 is much better than TPACKET_V2, but for TSO packet, it is bad, we prefer to use TPACKET_V3 for better performance.

At high rate, blocks are retired and userspace is notified as soon as a packet arrives that does not fit and requires dispatching a new block. As such, max throughput is not timer dependent. The timer exists to bound notification latency when packet arrival rate is slow.

[Yi Yang] Per our iperf3 tcp test with TSO enabled, even if packet size is about 64K and block size is also 64K + 4K (to accommodate tpacket_vX header), we can't see high performance without this patch, I think some small packets before 64K big packets decide what performance it can reach, according to my trace, TCP packet size is increasing from less than 100 to 64K gradually, so it looks like how long this period took decides what performance it can reach. So yes, I don’t think hrtimer can help fix this issue very efficiently. In addition, I also noticed packet size pattern is 1514, 64K, 64K, 64K, 64K, ..., 1514, 64K even if it reaches 64K packet size, maybe that 1514 packet has big impact on performance, I just guess.

[Yi Yang] 

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