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<div>cons: large BDP in general would be negatively affected.
<div>A Gbps access vs a DSL access to the same server would require very different tuning. </div>
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<div>sch_fq would probably make the whole thing less of a problem. </div>
<div>But running it in a VM does not sound a good idea and would not reflect usual servers setting BTW </div>
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<div>-------- Message d'origine --------</div>
<div>De : Eric Dumazet </div>
<div>Date :2015/04/22 12:29 (GMT+08:00) </div>
<div>À : "Steinar H. Gunderson" </div>
<div>Cc : bloat </div>
<div>Objet : Re: [Bloat] DSLReports Speed Test has latency measurement built-in </div>
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<div class="PlainText">On Wed, 2015-04-22 at 06:04 +0200, Steinar H. Gunderson wrote:<br>
> On Tue, Apr 21, 2015 at 08:35:21PM +1000, jb wrote:<br>
> > As I understand it (I thought) SO_SNDBUF and SO_RCVBUF are socket buffers<br>
> > for the application layer, they do not change the TCP window size either<br>
> > send or receive.<br>
> <br>
> I haven't gone into the code and checked, but from practical experience I<br>
> think you're wrong. I've certainly seen positive effects (and verified with<br>
> tcpdump) from reducing SO_SNDBUF on a server that should have no problems at<br>
> all sending data really fast to the kernel.<br>
<br>
Well, using SO_SNDBUF disables TCP autotuning.<br>
<br>
Doing so :<br>
<br>
Pros:<br>
<br>
autotuning is known to enable TCP cubic to grow cwnd to bloat levels.<br>
With small enough SO_SNDBUF, you limit this cwnd increase.<br>
<br>
Cons:<br>
<br>
Long rtt sessions might not have enough packets to utilize bandwidth.<br>
<br>
<br>
> <br>
> Then again, this kind of manual tuning trickery got obsolete for me the<br>
> moment sch_fq became available.<br>
<br>
Note that I suppose the SO_MAX_PACING rate is really helping you.<br>
<br>
Without it, TCP cubic is still allowed to 'fill the pipes' until packet<br>
losses.<br>
<br>
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