Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <bf0cced86a1466285f74eb845e73fbaea1dff1c0.camel@sipsolutions.net>
Subject: Re: debugging TXQs being empty
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Kan Yan <kyan@google.com>
Cc:     Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@redhat.com>,
        linux-wireless <linux-wireless@vger.kernel.org>
Date:   Fri, 06 Dec 2019 10:12:59 +0100
In-Reply-To: <9b89b3b294295063aec045b9e863a44ad20b8782.camel@sipsolutions.net> (sfid-20191206_094144_773877_4A5AF79B)
References: <bbc516f28782175b27ac5e19dcdeac13cd6ee76a.camel@sipsolutions.net>
         <fd23a26dea59128ede8c1c4d02fb2f3514ffb5e9.camel@sipsolutions.net>
         <CA+iem5tjTpO_2MKL_pEu7enTa-8=g5vY3=2WJKjg9f=JA2eCEw@mail.gmail.com>
         (sfid-20191206_020554_916514_C4D7D41E) <9b89b3b294295063aec045b9e863a44ad20b8782.camel@sipsolutions.net>
         (sfid-20191206_094144_773877_4A5AF79B)
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.34.2 (3.34.2-1.fc31) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On Fri, 2019-12-06 at 09:41 +0100, Johannes Berg wrote:
> 
> Maybe somehow TSO is interacting badly with the TXQs and the tracking
> here, since TSO makes the traffic *very* bursty? A 64k packet in the
> driver will typically expand to 9 or 10 A-MSDUs I think?

No, that all seems well. Without TSO (with the trivial mac80211 patch to
let me turn it off with ethtool) I get about 890Mbps, so about 5% less.
That's not actually *that* bad, I guess due to software A-MSDU in
mac80211, but it's not really the right direction :)

Changing wmem_max/tcp_mem to outrageous values also didn't really make
any difference.

I guess it's time to see if I can poke into the TCP stack to figure out
what's going on...

johannes