[gentoo-user] Re: Steam downloading extremely

[Kai Krakow]

Am Wed, 15 Mar 2017 21:24:10 +0800
schrieb Danny YUE <sheepduke@×××××.com>:

> Hi guys,
>
> I just got Steam installed and running successfully on my machine,
> and tried to get CS:GO running smoothly, which made me really
> happy :-D
>
> However when Steam is downloading games, the speed is extremely slow,
> down to several KB/s, even some bytes/s.
> I have already installed dnsmasq and it *was* good during downloading
> CS:GO (~4MB/s), but became slow again with Civilization V.
>
> I googled a lot but all point to installing dnsmasq, which I don't
> think is really helpful since I already have done that...
>
> Also I'm sure downloading region is correct.
>
> Anybody experienced the same issue with dnsmasq installed?
> Any clue is welcome and thanks in advance.

Here, it's downloading with peak bandwidths of 48 mbytes/s but usually
it's around 38 mbytes/s. However, I sometimes see slowdowns, too. I
guess that games are downloaded file by file, and when a lot of small
files are left in the queue, it just cannot get good bandwidth.

But I only see such slowdowns mostly short before the last few
megabytes of a game.

Could you check if your downloaded games consist of many smallish
files? Then that could be the explanation.

You could try activating fq_codel and tcp fastopen:

In /proc/sys/net/ipv4/tcp_fastopen it should say 1.
In /proc/sys/net/core/default_qdisc it should say fq_codel.

Also, you may want to try out bbr congestion control:

In /proc/sys/net/ipv4/tcp_congestion_control it should say bbr.

By recompiling the kernel, you can reconfigure the defaults for this
(and enable support). Some of these need modern kernels.

Additionally, many small tcp request need a good portion of your upload
bandwidth and are very dependent on good round trip times. Traditional
DSL lines with ping times of 50-60ms can really slow down requests of
small files a lot due to three-way tcp handshaking, that is, you could
request only one smallish file per 100-120ms. This can totally destroy
the usable bandwidth. Maybe watch a running ping while the downloads
are running. If the ping times increase while the download slows down,
your bottleneck is the upload.

But also keep in mind that traditional spinning disks may not keep up
with the bandwidth if confronted with many small files. If you're using
SSD all should be fine. I'm running on bcache with writeback caching
which gives a really good performance boost by adding a small SSD to
one or more big HDDs.

-- 
Regards,
Kai

Replies to list-only preferred.