From: Eric Dumazet <eric.dumazet@gmail.com>
To: Weiping Pan <panweiping3@gmail.com>
Cc: netdev@vger.kernel.org, edumazet@google.com
Subject: Re: [PATCH] tcp: refine autocork condition check
Date: Wed, 15 Oct 2014 04:47:49 -0700 [thread overview]
Message-ID: <1413373669.17365.25.camel@edumazet-glaptop2.roam.corp.google.com> (raw)
In-Reply-To: <8e0610510498c7f6ecbe2e99ab6044030f93f792.1413369212.git.panweiping3@gmail.com>
On Wed, 2014-10-15 at 18:34 +0800, Weiping Pan wrote:
> Inspired by commit b2532eb9abd8 (tcp: fix ooo_okay setting vs Small Queues).
>
> The last check in tcp_should_autocork() was meant to check that whether we
> only have an ACK in Qdisc/NIC queues, or if TX completion was delayed after we
> processed ACK packet, if so, we should push the packet immediately instead of
> corking it.
> Therefore we should compare sk_wmem_alloc with SKB_TRUESIZE(1) instead of
> skb->truesize.
>
> After this patch, tcp should have more chances to be corked, and the
> performance should be a little better. And netperf shows that this patch
> works as expected.
>
> ./super_netperf.sh 300 -H 10.16.42.249 -t TCP_STREAM -- -m 1 -M 1
> speed TCPAutoCorking
> Before patch: 169.38 222278
> After patch: 173.27 232988
>
I do not see how this patch changes anything on this workload, I suspect
noise in your tests ? Full nstat output would give some hints maybe.
TCP_STREAM netperfs send no ACK packets at all.
I am concerned that this patch adds some latencies, and this wont be
seen with your TCP_STREAM test.
Autocorking is a trade off between throughput and latencies.
We need extensive tests, using TCP_RR with various sizes.
Existing behavior is telling that if a prior packet is in qdisc, and
this skb has a bigger truesize, we do not autocork.
In practice, you might hold now packets that are quite big, (more than
SKB_WITH_OVERHEAD(2048 - MAX_TCP_HEADER) bytes of payload.
Typical cases is applications using two writes, one to send a small
header, one for the body of the request/answer.
Existing code is better because we allow the second send() to be pushed
to the qdisc/NIC, before first send is TX completed.
next prev parent reply other threads:[~2014-10-15 11:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-15 10:34 [PATCH] tcp: refine autocork condition check Weiping Pan
2014-10-15 11:47 ` Eric Dumazet [this message]
2014-10-18 9:22 ` Weiping Pan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1413373669.17365.25.camel@edumazet-glaptop2.roam.corp.google.com \
--to=eric.dumazet@gmail.com \
--cc=edumazet@google.com \
--cc=netdev@vger.kernel.org \
--cc=panweiping3@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).