[Cerowrt-devel] [Bug #442] < vs <= in two comparisons

[Dave Taht]

Could part of it be as simple as not checking for '<='  but only < in
txq_max_pending below?

in ath_tx_start:

ath_txq_lock(sc, txq);
if (txq == sc->tx.txq_map[q] &&
++txq->pending_frames > sc->tx.txq_max_pending[q] &&
!txq->stopped) {
ieee80211_stop_queue(sc->hw, q);
txq->stopped = true;
}

in ath_txq_skb_done:

if (txq->stopped &&
txq->pending_frames < sc->tx.txq_max_pending[q]) {
ieee80211_wake_queue(sc->hw, q);
txq->stopped = false;
}


-- 
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Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Greg White]

On 4/18/14, 1:05 PM, "Dave Taht"  wrote:

>On Fri, Apr 18, 2014 at 11:15 AM, Greg White 
>wrote:
>>
>> The choice of RTTs also came from the web traffic captures. I saw
>> RTTmin=16ms, RTTmean=53.8ms, RTTmax=134ms.
>
>Get a median?

Median value was 62ms.

>
>My own stats are probably quite skewed lower from being in california,
>and doing some tests from places like isc.org in redwood city, which
>is insanely well
>co-located.

Mine are probably skewed too. I was told that global median (at the time I
collected this data) was around 100ms.

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Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Dave Taht]

> The specific thing I've been concerned about was not the probability of
> a dns loss, although as you note the consequences are huge -
> but the frequency and cost of a cache miss and the resulting fill.
>
> This is a very simple namebench test against the alexa top 1000:
>
> http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-20_1255.html
>
> This is a more comprehensive one taken against my own recent web history file.
>
> http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-24_1541.html
>
> Both of these were taken against the default SQM system in cerowrt
> against a cable modem, so you can
> pretty safely assume the ~20ms (middle) knee in the curve is basically
> based on physical
> RTT to the nearest upstream DNS server.
>
> And it's a benchmark so I don't generally believe in the relative hit
> ratios vs a vs "normal traffic", but do think the baseline RTT, and
> the knees in the curves in the cost of a miss and file are relevant.

To be utterly clear here, the ~20ms knee in this data is a variable dependent
on the RTT to the nearest upstream DNS server. Most - nearly all -
ISPs - have a hefty dns server in their co-location facility, but the
baseline physical RTT is dependent on the actual technology in use.

The actual RTT of an query is dependent on the outstanding queue
length in a single queue AQM, unless otherwise prioritized. If prioritized
(cerowrt's 3 band system does this for queries coming from the router)
I imagine the packet loss rate drops hugely, also.

To give an extreme example of the DNS rtt problem, dns lookups over
satellite links take
800+ms, and this is one reason why web proxy servers are so common
in such environments as the whole query is shipped to a local-to-the-internet
proxy server so as to avoid this rtt cost. This technique is of increasingly
limited value in an age of e2e encryption.

Also: recently we've seen increasing use of non-local or otherwise redirected
dns servers such as here

http://www.cnet.com/news/google-confirms-turkey-is-blocking-its-dns-service/

It would be a good research project for someone to catagorize typical
nearest-upstream DNS RTTs, the availability of local-to-site dns
servers, hit/miss ratios
in homes and small business, the cost of dnssec, etc.


-- 
Dave Täht

NSFW: 
https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_indecent.article
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Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Greg White]

In most cases it was *far* less than 1%.  In our DOCSIS 3.1 scenarios it is 
more like 1e-5 to 1e-4 (1e-3 worst case for the bufferbloated drop tail 
baseline) which means that implementing dns in the model would have affected on 
the order of 1 out of every 2500 page loads.

As with any model of reality, there is a tradeoff between complexity and 
fidelity, right? We chose 4 servers as being a reasonable and practical number. 
 Many of the most popular sites actually don't distribute content that widely 
(e.g. Google only used 3 servers in our measurements), and the worst case was 
32 servers.   In reality every web page is different, and you could come up 
with an arbitrarily complex model and it still wouldn't match some version of 
reality.  In my view, we want to have something that is practical to implement 
and close enough to reality to be useful.  In the AQM-evaluation draft 
currently, the model is a single 700kB file served from a single server.

Greg

From: "dpr...@reed.com" 
mailto:dpr...@reed.com>>
Date: Friday, April 18, 2014 at 12:48 PM
To: Greg White mailto:g.wh...@cablelabs.com>>
Cc: Dave Taht mailto:dave.t...@gmail.com>>, "William Chan 
(陈智昌)" mailto:willc...@chromium.org>>, 
"a...@ietf.org" mailto:a...@ietf.org>>, 
"cerowrt-devel@lists.bufferbloat.net"
 
mailto:cerowrt-devel@lists.bufferbloat.net>>,
 bloat mailto:bl...@lists.bufferbloat.net>>
Subject: Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed


Why is the DNS PLR so high?  1% is pretty depressing.



Also, it seems odd to eliminate 19% of the content retrieval because the tail 
is fat and long rather than short.  Wouldn't it be better to have 1000 servers?






On Friday, April 18, 2014 2:15pm, "Greg White" 
mailto:g.wh...@cablelabs.com>> said:


> Dave,
>
> We used the 25k object size for a short time back in 2012 until we had
> resources to build a more advanced model (appendix A). I did a bunch of
> captures of real web pages back in 2011 and compared the object size
> statistics to models that I'd seen published. Lognormal didn't seem to be
> *exactly* right, but it wasn't a bad fit to what I saw. I've attached a
> CDF.
>
> The choice of 4 servers was based somewhat on logistics, and also on a
> finding that across our data set, the average web page retrieved 81% of
> its resources from the top 4 servers. Increasing to 5 servers only
> increased that percentage to 84%.
>
> The choice of RTTs also came from the web traffic captures. I saw
> RTTmin=16ms, RTTmean=53.8ms, RTTmax=134ms.
>
> Much of this can be found in
> https://tools.ietf.org/html/draft-white-httpbis-spdy-analysis-00
>
> In many of the cases that we've simulated, the packet drop probability is
> less than 1% for DNS packets. In our web model, there are a total of 4
> servers, so 4 DNS lookups assuming none of the addresses are cached. If
> PLR = 1%, there would be a 3.9% chance of losing one or more DNS packets
> (with a resulting ~5 second additional delay on load time). I've probably
> oversimplified this, but Kathie N. and I made the call that it would be
> significantly easier to just do this math than to build a dns
> implementation in ns2. We've open sourced the web model (it's on Kathie's
> web page and will be part of ns2.36) with an encouragement to the
> community to improve on it. If you'd like to port it to ns3 and add a dns
> model, that would be fantastic.
>
> -Greg
>
>
> On 4/17/14, 3:07 PM, "Dave Taht" 
> mailto:dave.t...@gmail.com>> wrote:
>
> >On Thu, Apr 17, 2014 at 12:01 PM, William Chan (陈智昌)
> >mailto:willc...@chromium.org>> wrote:
> >> Speaking as the primary Chromium developer in charge of this relevant
> >>code,
> >> I would like to caution putting too much trust in the numbers
> >>generated. Any
> >> statistical claims about the numbers are probably unreasonable to make.
> >
> >Sigh. Other benchmarks such as the apache ("ab") benchmark
> >are primarily designed as stress testers for web servers, not as realistic
> >traffic. Modern web traffic has such a high level of dynamicism in it,
> >that static web page loads along any distribution, seem insufficient,
> >passive analysis of aggregated traffic "feels" incorrect relative to the
> >sorts of home and small business traffic I've seen, and so on.
> >
> >Famous papers, such as this one:
> >
> >http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-leland.pdf
> >
> >Seem possibly irrelevant to draw conclusions from given the kind
> >of data they analysed and proceeding from an incorrect model or
> >gut feel for how the network behaves today seems to be foolish.
> >
> >Even the most basic of tools, such as httping, had three basic bugs
> >that I found in a few minutes of trying to come up with some basic
> >behaviors yesterday:
> >
> >https://lists.bufferbloat.net/pipermail/bloat/2014-April/001890.html
> >
> >Those are going to be a lot easier to fix than diving into the chromium
> >codebase!
> 

Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Dave Taht]

On Fri, Apr 18, 2014 at 11:15 AM, Greg White  wrote:
> Dave,
>
> We used the 25k object size for a short time back in 2012 until we had
> resources to build a more advanced model (appendix A).  I did a bunch of
> captures of real web pages back in 2011 and compared the object size
> statistics to models that I'd seen published.  Lognormal didn't seem to be
> *exactly* right, but it wasn't a bad fit to what I saw.  I've attached a
> CDF.

That does seem a bit large on the initial 20%.

Hmm.

There is a second kind of major case, where you are
moving around on the same web property, and hopefully many
core portions of the web page(s) such as the css and javascript,
basic logos and other images, are cached. Caching is handled
two ways, one is to explicitly mark the data as cacheable for
a certain period, the other is an if-modified-since request,
which costs RTTs for setup and the query. I am
under the impression that we generally see a lot more of the
latter than the former these days.

> The choice of 4 servers was based somewhat on logistics, and also on a
> finding that across our data set, the average web page retrieved 81% of
> its resources from the top 4 servers.  Increasing to 5 servers only
> increased that percentage to 84%.
>
> The choice of RTTs also came from the web traffic captures. I saw
> RTTmin=16ms, RTTmean=53.8ms, RTTmax=134ms.

Get a median?

My own stats are probably quite skewed lower from being in california,
and doing some tests from places like isc.org in redwood city, which
is insanely well
co-located.

> Much of this can be found in
> https://tools.ietf.org/html/draft-white-httpbis-spdy-analysis-00

Thx!

> In many of the cases that we've simulated, the packet drop probability is
> less than 1% for DNS packets.  In our web model, there are a total of 4

I think we have the ability to get a better number for dns loss now.

> servers, so 4 DNS lookups assuming none of the addresses are cached. If
> PLR = 1%, there would be a 3.9% chance of losing one or more DNS packets
> (with a resulting ~5 second additional delay on load time).  I've probably
> oversimplified this, but Kathie N. and I made the call that it would be
> significantly easier to just do this math than to build a dns
> implementation in ns2.


The specific thing I've been concerned about was not the probability of
a dns loss, although as you note the consequences are huge -
but the frequency and cost of a cache miss and the resulting fill.

This is a very simple namebench test against the alexa top 1000:

http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-20_1255.html

This is a more comprehensive one taken against my own recent web history file.

http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-24_1541.html

Both of these were taken against the default SQM system in cerowrt
against a cable modem, so you can
pretty safely assume the ~20ms (middle) knee in the curve is basically
based on physical
RTT to the nearest upstream DNS server.

And it's a benchmark so I don't generally believe in the relative hit
ratios vs a vs "normal traffic", but do think the baseline RTT, and
the knees in the curves in the cost of a miss and file are relevant.

(it's also not clear to me if all cable modems run a local dns server)

Recently simon kelly added support for gathering hit and miss
statistics to dnsmasq 2.69.

They can be obtained via  a simple dns lookup as answers to queries of
class CHAOS and type TXT in domain bind. The domain names are
cachesize.bind, insertions.bind, evictions.bind, misses.bind,
hits.bind, auth.bind and servers.bind. An example command to query
this, using the dig utility would be

dig +short chaos txt cachesize.bind

It would be very interesting to see the differences between dnsmasq
without DNSSEC, with DNSSEC and with DNSSEC and
--dnssec-check-unsigned (checking for proof of non-existence) - we've
been a bit concerned about the overheads of the last in particular.

Getting more elaborate stats (hit, miss, and fill costs) is under discussion.

> We've open sourced the web model (it's on Kathie's
> web page and will be part of ns2.36) with an encouragement to the
> community to improve on it.  If you'd like to port it to ns3 and add a dns
> model, that would be fantastic.

As part of the google summer of code I am signed up to mentor a
student with tom for the *codel related bits
in ns3, and certainly plan to get fingers dirty in the cablelabs drop,
and there was a very encouraging patch set distributed around for
tcp-cubic with hystart support recently as well as a halfway decent
802.11 mac emulation.

As usual, I have no funding, personally, to tackle the job, but I'll
do what I can anyway. It would be wonderful to finally have all the
ns2 and ns3 code mainlined for more people to use it.



-- 
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Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[dpreed]

Why is the DNS PLR so high?  1% is pretty depressing.
 
Also, it seems odd to eliminate 19% of the content retrieval because the tail 
is fat and long rather than short.  Wouldn't it be better to have 1000 servers?
 
 


On Friday, April 18, 2014 2:15pm, "Greg White"  said:



> Dave,
> 
> We used the 25k object size for a short time back in 2012 until we had
> resources to build a more advanced model (appendix A).  I did a bunch of
> captures of real web pages back in 2011 and compared the object size
> statistics to models that I'd seen published.  Lognormal didn't seem to be
> *exactly* right, but it wasn't a bad fit to what I saw.  I've attached a
> CDF.
> 
> The choice of 4 servers was based somewhat on logistics, and also on a
> finding that across our data set, the average web page retrieved 81% of
> its resources from the top 4 servers.  Increasing to 5 servers only
> increased that percentage to 84%.
> 
> The choice of RTTs also came from the web traffic captures. I saw
> RTTmin=16ms, RTTmean=53.8ms, RTTmax=134ms.
> 
> Much of this can be found in
> https://tools.ietf.org/html/draft-white-httpbis-spdy-analysis-00
> 
> In many of the cases that we've simulated, the packet drop probability is
> less than 1% for DNS packets.  In our web model, there are a total of 4
> servers, so 4 DNS lookups assuming none of the addresses are cached. If
> PLR = 1%, there would be a 3.9% chance of losing one or more DNS packets
> (with a resulting ~5 second additional delay on load time).  I've probably
> oversimplified this, but Kathie N. and I made the call that it would be
> significantly easier to just do this math than to build a dns
> implementation in ns2.  We've open sourced the web model (it's on Kathie's
> web page and will be part of ns2.36) with an encouragement to the
> community to improve on it.  If you'd like to port it to ns3 and add a dns
> model, that would be fantastic.
> 
> -Greg
> 
> 
> On 4/17/14, 3:07 PM, "Dave Taht"  wrote:
> 
> >On Thu, Apr 17, 2014 at 12:01 PM, William Chan (陈智昌)
> > wrote:
> >> Speaking as the primary Chromium developer in charge of this relevant
> >>code,
> >> I would like to caution putting too much trust in the numbers
> >>generated. Any
> >> statistical claims about the numbers are probably unreasonable to make.
> >
> >Sigh. Other benchmarks such as the apache ("ab") benchmark
> >are primarily designed as stress testers for web servers, not as realistic
> >traffic. Modern web traffic has such a high level of dynamicism in it,
> >that static web page loads along any distribution, seem insufficient,
> >passive analysis of aggregated traffic "feels" incorrect relative to the
> >sorts of home and small business traffic I've seen, and so on.
> >
> >Famous papers, such as this one:
> >
> >http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-leland.pdf
> >
> >Seem possibly irrelevant to draw conclusions from given the kind
> >of data they analysed and proceeding from an incorrect model or
> >gut feel for how the network behaves today seems to be foolish.
> >
> >Even the most basic of tools, such as httping, had three basic bugs
> >that I found in a few minutes of trying to come up with some basic
> >behaviors yesterday:
> >
> >https://lists.bufferbloat.net/pipermail/bloat/2014-April/001890.html
> >
> >Those are going to be a lot easier to fix than diving into the chromium
> >codebase!
> >
> >There are very few tools worth trusting, and I am always dubious
> >of papers that publish results with unavailable tools and data. The only
> >tools I have any faith in for network analysis are netperf,
> >netperf-wrapper,
> >tcpdump and xplot.org, and to a large extent wireshark. Toke and I have
> >been tearing apart d-itg and I hope to one day be able to add that to
> >my trustable list... but better tools are needed!
> >
> >Tools that I don't have a lot of faith in include that, iperf, anything
> >written
> >in java or other high level languages, speedtest.net, and things like
> >shaperprobe.
> >
> >Have very little faith in ns2, slightly more in ns3, and I've been meaning
> >to look over the mininet and other simulators whenever I got some spare
> >time; the mininet results stanford gets seem pretty reasonable and I
> >adore their reproducing results effort. Haven't explored ndt, keep meaning
> >to...
> >
> >> Reasons:
> >> * We don't actively maintain this code. It's behind the command line
> >>flags.
> >> They are broken. The fact that it still results in numbers on the
> >>benchmark
> >> extension is an example of where unmaintained code doesn't have the UI
> >> disabled, even though the internal workings of the code fail to
> >>guarantee
> >> correct operation. We haven't disabled it because, well, it's
> >>unmaintained.
> >
> >As I mentioned I was gearing up for a hacking run...
> >
> >The vast majority of results I look at are actually obtained via
> >looking at packet captures. I mostly use benchmarks as abstractions
> >to see if they make some sense relative to the captures a

Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Greg White]

Dave, 

We used the 25k object size for a short time back in 2012 until we had
resources to build a more advanced model (appendix A).  I did a bunch of
captures of real web pages back in 2011 and compared the object size
statistics to models that I'd seen published.  Lognormal didn't seem to be
*exactly* right, but it wasn't a bad fit to what I saw.  I've attached a
CDF.

The choice of 4 servers was based somewhat on logistics, and also on a
finding that across our data set, the average web page retrieved 81% of
its resources from the top 4 servers.  Increasing to 5 servers only
increased that percentage to 84%.

The choice of RTTs also came from the web traffic captures. I saw
RTTmin=16ms, RTTmean=53.8ms, RTTmax=134ms.

Much of this can be found in
https://tools.ietf.org/html/draft-white-httpbis-spdy-analysis-00

In many of the cases that we've simulated, the packet drop probability is
less than 1% for DNS packets.  In our web model, there are a total of 4
servers, so 4 DNS lookups assuming none of the addresses are cached. If
PLR = 1%, there would be a 3.9% chance of losing one or more DNS packets
(with a resulting ~5 second additional delay on load time).  I've probably
oversimplified this, but Kathie N. and I made the call that it would be
significantly easier to just do this math than to build a dns
implementation in ns2.  We've open sourced the web model (it's on Kathie's
web page and will be part of ns2.36) with an encouragement to the
community to improve on it.  If you'd like to port it to ns3 and add a dns
model, that would be fantastic.

-Greg


On 4/17/14, 3:07 PM, "Dave Taht"  wrote:

>On Thu, Apr 17, 2014 at 12:01 PM, William Chan (陈智昌)
> wrote:
>> Speaking as the primary Chromium developer in charge of this relevant
>>code,
>> I would like to caution putting too much trust in the numbers
>>generated. Any
>> statistical claims about the numbers are probably unreasonable to make.
>
>Sigh. Other benchmarks such as the apache ("ab") benchmark
>are primarily designed as stress testers for web servers, not as realistic
>traffic. Modern web traffic has such a high level of dynamicism in it,
>that static web page loads along any distribution, seem insufficient,
>passive analysis of aggregated traffic "feels" incorrect relative to the
>sorts of home and small business traffic I've seen, and so on.
>
>Famous papers, such as this one:
>
>http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-leland.pdf
>
>Seem possibly irrelevant to draw conclusions from given the kind
>of data they analysed and proceeding from an incorrect model or
>gut feel for how the network behaves today seems to be foolish.
>
>Even the most basic of tools, such as httping, had three basic bugs
>that I found in a few minutes of trying to come up with some basic
>behaviors yesterday:
>
>https://lists.bufferbloat.net/pipermail/bloat/2014-April/001890.html
>
>Those are going to be a lot easier to fix than diving into the chromium
>codebase!
>
>There are very few tools worth trusting, and I am always dubious
>of papers that publish results with unavailable tools and data. The only
>tools I have any faith in for network analysis are netperf,
>netperf-wrapper,
>tcpdump and xplot.org, and to a large extent wireshark. Toke and I have
>been tearing apart d-itg and I hope to one day be able to add that to
>my trustable list... but better tools are needed!
>
>Tools that I don't have a lot of faith in include that, iperf, anything
>written
>in java or other high level languages, speedtest.net, and things like
>shaperprobe.
>
>Have very little faith in ns2, slightly more in ns3, and I've been meaning
>to look over the mininet and other simulators whenever I got some spare
>time; the mininet results stanford gets seem pretty reasonable and I
>adore their reproducing results effort. Haven't explored ndt, keep meaning
>to...
>
>> Reasons:
>> * We don't actively maintain this code. It's behind the command line
>>flags.
>> They are broken. The fact that it still results in numbers on the
>>benchmark
>> extension is an example of where unmaintained code doesn't have the UI
>> disabled, even though the internal workings of the code fail to
>>guarantee
>> correct operation. We haven't disabled it because, well, it's
>>unmaintained.
>
>As I mentioned I was gearing up for a hacking run...
>
>The vast majority of results I look at are actually obtained via
>looking at packet captures. I mostly use benchmarks as abstractions
>to see if they make some sense relative to the captures and tend
>to compare different benchmarks against each other.
>
>I realize others don't go into that level of detail, so you have given
>fair warning! In our case we used the web page benchmarker as
>a means to try and rapidly acquire some typical distributions of
>get and tcp stream requests from things like the alexa top 1000,
>and as a way to A/B different aqm/packet scheduling setups.
>
>... but the only easily publishable results were from the benchmark
>itself,
>and we (reluct

[Cerowrt-devel] ZDnet & Linksys WRT1900AC

[Rich Brown]

Larry Seltzer at ZDnet.com posted a short note about the new Linksys router. I 
posted a response.

http://www.zdnet.com/first-look-belkin-revives-updates-linksys-wrt-router-728561/

I'm trying to send Larry a direct response so he can ask more questions if he's 
interested.

Rich
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