From: Jim Gettys <jg@freedesktop.org>
To: Avery Pennarun <apenwarr@google.com>
Cc: "dstanley@arubanetworks.com" <dstanley@arubanetworks.com>,
Andrew McGregor <andrewmcgr@gmail.com>,
Stig Thormodsrud <stig@ubnt.com>,
netdev@vger.kernel.org,
linux-wireless <linux-wireless@vger.kernel.org>,
Jesper Dangaard Brouer <jbrouer@redhat.com>,
"cerowrt-devel@lists.bufferbloat.net"
<cerowrt-devel@lists.bufferbloat.net>,
Matt Mathis <mattmathis@google.com>,
Derrick Pallas <pallas@meraki.com>,
Kathy Giori <kgiori@qca.qualcomm.com>,
Mahesh Paolini-Subramanya <mahesh@dieswaytoofast.com>,
Jonathan Morton <chromatix99@gmail.com>,
Tim Shepard <shep@alum.mit.edu>
Subject: Re: [Cerowrt-devel] Fwd: Throughput regression with `tcp: refine TSO autosizing`
Date: Mon, 2 Feb 2015 10:25:45 -0500 [thread overview]
Message-ID: <CAGhGL2CnECP=3JkYEeshjqh7p1ra1jUunvVkSDQftGA+CVrPug@mail.gmail.com> (raw)
In-Reply-To: <CAPp0ZBbKu-B3yPf0Et=XByJ1SrnxBgVbRXr9PBe0f6P08w87=Q@mail.gmail.com>
On Sun, Feb 1, 2015 at 11:04 PM, Avery Pennarun <apenwarr@google.com> wrote:
> On Sun, Feb 1, 2015 at 6:34 PM, Andrew McGregor <andrewmcgr@gmail.com> wrote:
>> I missed one item in my list of potential improvements: the most braindead
>> thing 802.11 has to say about rates is that broadcast and multicast packets
>> should be sent at 'the lowest basic rate in the current supported rate set',
>> which is really wasteful. There are a couple of ways of dealing with this:
>> one, ignore the standard and pick the rate that is most likely to get the
>> frame to as many neighbours as possible (by a scan of the Minstrel tables).
>> Or two, fan it out as unicast, which might well take less airtime (due to
>> aggregation) as well as being much more likely to be delivered, since you
>> get ACKs and retries by doing that.
>
> As far as I can see, the only sensible thing to do with
> multicast/broadcast is some variation of the unicast fanout, unless
> you've got a truly huge number of nodes. I don't know of any
> protocols (certainly not video streams) that actually work well with
> the kind of packet loss you see at medium/long range with wifi if
> retransmits aren't used. I've heard that openwrt already has a patch
> included that does this kind of fanout at the bridge layer.
I gather some Windows drivers from some vendors do this unicast fanout
(claim made by one of their engineers in an early homenet meeting).
>
> I've also heard of a new "reliable multicast" in some newer 802.11
> variant, which essentially sends out a single multicast packet and
> expects an ACK from each intended recipient. Other than adding
> complexity, it seems like the best of both worlds.
So long as it times out in some very small, finite time. We don't
want a repeat of the infinite retry bugs Dave found in drivers a few
years back...
"Reliable multicast" ultimately is an oxymoron, particularly on a
medium with hundreds/one bandwidth variation. One remote low
bandwidth station cannot be allowed to drag the entire network to the
basement.
- Jim
next prev parent reply other threads:[~2015-02-02 15:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CA+BoTQkVu23P3EOmY_Q3E1GJnWsyF==Pawz4iPOS_Bq5dvfO5Q@mail.gmail.com>
[not found] ` <1422537297.21689.15.camel@edumazet-glaptop2.roam.corp.google.com>
[not found] ` <54CB5D08.2070906@broadcom.com>
[not found] ` <1422623975.21689.77.camel@edumazet-glaptop2.roam.corp.google.com>
[not found] ` <54CB8B69.1070807@broadcom.com>
[not found] ` <CAA93jw5fqhz0Hiw74L2GXgtZ9JsMg+NtYydKxKzGDrvQcZn4hA@mail.gmail.com>
2015-01-31 21:05 ` Dave Taht
2015-01-31 21:51 ` dpreed
2015-02-01 3:06 ` Avery Pennarun
2015-02-01 8:07 ` Andrew McGregor
2015-02-01 8:45 ` Dave Taht
2015-02-01 10:47 ` Jonathan Morton
2015-02-01 14:43 ` dpreed
2015-02-01 23:34 ` Andrew McGregor
2015-02-02 4:04 ` Avery Pennarun
2015-02-02 15:25 ` Jim Gettys [this message]
2015-02-02 4:21 ` Avery Pennarun
2015-02-02 7:07 ` David Lang
2015-02-02 16:22 ` dpreed
2015-02-02 18:29 ` David Lang
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
List information: https://lists.bufferbloat.net/postorius/lists/cerowrt-devel.lists.bufferbloat.net/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAGhGL2CnECP=3JkYEeshjqh7p1ra1jUunvVkSDQftGA+CVrPug@mail.gmail.com' \
--to=jg@freedesktop.org \
--cc=andrewmcgr@gmail.com \
--cc=apenwarr@google.com \
--cc=cerowrt-devel@lists.bufferbloat.net \
--cc=chromatix99@gmail.com \
--cc=dstanley@arubanetworks.com \
--cc=jbrouer@redhat.com \
--cc=kgiori@qca.qualcomm.com \
--cc=linux-wireless@vger.kernel.org \
--cc=mahesh@dieswaytoofast.com \
--cc=mattmathis@google.com \
--cc=netdev@vger.kernel.org \
--cc=pallas@meraki.com \
--cc=shep@alum.mit.edu \
--cc=stig@ubnt.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