linux-kernel - Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY

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Message-ID: <155a86d5-a910-c366-f521-216a0582bad8@gmail.com>
Date:   Wed, 25 Apr 2018 09:35:10 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for
 zerocopy receive



On 04/25/2018 09:22 AM, Andy Lutomirski wrote:

> In general, I suspect that the zerocopy receive mechanism will only
> really be a win in single-threaded applications that consume large
> amounts of receive bandwidth on a single TCP socket using lots of
> memory and don't do all that much else.

This was dully noted in the original patch submission.

https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=309c446cb45f6663932c8e6d0754f4ac81d1b5cd

Our intent at Google is to use it for some specific 1MB+ receives, not as a generic and universal mechanism.

The major benefit is really the 4KB+ MTU, allowing to pack exactly 4096 bytes of payload per page.