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Message-ID: <1392066100.6615.55.camel@edumazet-glaptop2.roam.corp.google.com>
Date: Mon, 10 Feb 2014 13:01:40 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: Thomas Glanzmann <thomas@...nzmann.de>
Cc: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
John Ogness <john.ogness@...utronix.de>,
Eric Dumazet <edumazet@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
target-devel <target-devel@...r.kernel.org>,
Linux Network Development <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] This extends tx_data and and iscsit_do_tx_data with the
additional parameter flags and avoids sending multiple TCP packets in
iscsit_fe_sendpage_sg
On Mon, 2014-02-10 at 21:56 +0100, Thomas Glanzmann wrote:
> Hello Nab,
>
> > This looks correct to me. Thomas, once your able to confirm please
> > include your 'Tested-by' and I'll include for the next -rc3 PULL
> > request.
>
> Eric is currently reviewing our latest iteration with MSG_MORE for
> kernel_sendmsg and MSG_MORE | MSG_SENDPAGE_NOTLAST for sendpage. However
> with the last iteration we had again a high RTT for some packets. But
> than Eric let me tune net.ipv4.tcp_min_tso_segs to 8 and the RTT went
> down to what it used before auto corking was enabled. At least almost.
>
Hmm.. I was not aware of high RTT for some packets.
Can you spot this on the pcap you provided ?
> I'm having a steep learning curve but Eric hopefully knows how to get
> this back in check. Nevertheless the regression I saw are history
> because I saw that Eric has submitted the patch to David S. Miller which
> fixes the two bugs that killed the iSCSI performance when tcp auto
> corking was on. So currently we're just optimizing to get the last 20%
> or so out of it. Quite interesting. Especially how much bandwidth can be
> saved by coalescing packets.
It depends on the ratio payload/headers.
The beginning of your pcap show a lot of 512 bytes requests, so for this
kind of requests, the gain is huge (maybe 50%), but for 32K or 64K
request, gain would be marginal.
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