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8.1.0 download slower than 8.0.1 #11162

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pandada8 opened this issue May 20, 2023 · 6 comments
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8.1.0 download slower than 8.0.1 #11162

pandada8 opened this issue May 20, 2023 · 6 comments
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HTTP/2 performance

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@pandada8
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I did this

When download from same url with same network, curl 8.1.0 downloads half as fast as curl 8.0.1

pan@panda-router ~ ❯❯❯ curl 'https://mirrors.tuna.tsinghua.edu.cn/archlinux/iso/latest/archlinux-2023.05.03-x86_64.iso' -o /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  813M  100  813M    0     0  94.2M      0  0:00:08  0:00:08 --:--:-- 95.8M
pan@panda-router ~ ❯❯❯ curl 'https://mirrors.tuna.tsinghua.edu.cn/archlinux/iso/latest/archlinux-2023.05.03-x86_64.iso' -o /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  813M  100  813M    0     0  45.4M      0  0:00:17  0:00:17 --:--:-- 47.0M

(try a nearby mirror to test if you want to replicate, the provided link speed may be not optimal in your location)

I also tried different endpoint in a different location (vultr vps in la). It seems the slowdown ratio may be different, but 8.1.0 IS slower than 8.0.1

I expected the following

download speed shouldn't make any difference

curl/libcurl version

# curl -V
curl 8.1.0 (x86_64-pc-linux-gnu) libcurl/8.1.0 OpenSSL/3.0.8 zlib/1.2.13 brotli/1.0.9 zstd/1.5.5 libidn2/2.3.4 libpsl/0.21.2 (+libidn2/2.3.4) libssh2/1.10.0 nghttp2/1.53.0
Release-Date: 2023-05-17
Protocols: dict file ftp ftps gopher gophers http https imap imaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS brotli GSS-API HSTS HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM NTLM_WB PSL SPNEGO SSL threadsafe TLS-SRP UnixSockets zstd

I did some bisect, it seems the slowdown is introduced by 744dcf2
Indeed, the provided link is http2 enabled

operating system

Linux panda-router 6.2.11-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 13 Apr 2023 16:59:24 +0000 x86_64 GNU/Linux
@bagder bagder added the HTTP/2 label May 20, 2023
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bagder commented May 20, 2023

@pandada8 what's the average ping time client <=> server in this setup ?

@pandada8
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Around 3.5ms

@icing
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icing commented May 20, 2023

This seems to be the effect of the lower stream window size we introduced. I have a rather slow downlink, but I can see that the higher the ping time to a mirror, the less it becomes saturated. Increasing the http/2 window size - in the source - helps.

The relevant place in lib/http2.cis:

#define H2_STREAM_WINDOW_SIZE   (512 * 1024)

I would be interested to know what you experience when you increase that to 5 * 1024 * 1024. I assume you can build curl?

@pandada8
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I play around with different values, given 3.5ms latency

H2_STREAM_WINDOW_SIZE Download Speed
512 * 1024 50MB/s
5 * 512 * 1024 77MB/s
5 * 1024 * 1024 84MB/s
15 * 1024 * 1024 90.3MB/s
--http1.1 91.8MB/s

It does improve the performance, the final difference could be a margin of error

@icing
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icing commented May 20, 2023

Thanks for the measurements. Since I want a quick fix for the upcoming patch release, I suggest I settle for a 10MB window for now.

There might be a good way to adjust that more dynamically, but that is outside the current time frame.

icing added a commit to icing/curl that referenced this issue May 20, 2023
@icing
http/2, increase stream window size to 10 MB
c4ae416 
- refs curl#11162
@icing icing mentioned this issue May 20, 2023
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icing commented May 20, 2023

PR #11167 in CI now.

@bagder bagder closed this as completed in 1886eef May 20, 2023
bch pushed a commit to bch/curl that referenced this issue Jul 19, 2023
@icing @bch
http2: increase stream window size to 10 MB
8519fde 
Reported-by: pandada8 on github

Fixes curl#11162
Closes curl#11167
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