bugzilla-daemon at mindrot.org
2022-Nov-27 19:09 UTC
[Bug 3505] New: SSH_MSG_CHANNEL_WINDOW_ADJUST bottleneck
https://bugzilla.mindrot.org/show_bug.cgi?id=3505
Bug ID: 3505
Summary: SSH_MSG_CHANNEL_WINDOW_ADJUST bottleneck
Product: Portable OpenSSH
Version: -current
Hardware: Other
OS: All
Status: NEW
Severity: normal
Priority: P5
Component: Miscellaneous
Assignee: unassigned-bugs at mindrot.org
Reporter: mindrot at dimebar.com
tl;dr: Should we increase the maximum channel window size to allow
higher throughput for WAN data?
https://github.com/openssh/openssh-portable/commit/395ecc2bdeefd86a31562dd4145f370b816814bd
committed on 2007-06-12 is still the current #define for
CHAN_TCP_WINDOW_DEFAULT.
64*32*1024 = 2 MiB, but in 2022, I predict that networks are faster on
average than in 2007.
Some examples for 2 MiB BDP:
- 200ms @ 84 mbps
- 100ms @ 168 mbps
- 50ms @ 336 mbps
- 25ms @ 671 mbps
- 12ms @ 1398 mbps
- 6ms @ 2796 mbps
- 3ms @ 5592 mbps
Not everyone runs networks which exceed these parameters, but we do on
high-latency WANs.
The problem I'm seeing is the artificial bandwidth restriction
resulting from CHAN_TCP_WINDOW_DEFAULT being supplied to channel_new's
local_window_max.
It doesn't matter how much memory is given over to TCP buffers; because
OpenSSH (and scp, and rsync) receivers limit the channel window to
2MiB, an artificial speed limit exists.
After 15 years of
#define CHAN_TCP_WINDOW_DEFAULT (64*CHAN_TCP_PACKET_DEFAULT)
is it time for an increase? If not now, when? If not an increase,
perhaps a config option?
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bugzilla-daemon at mindrot.org
2023-Sep-14 11:40 UTC
[Bug 3505] SSH_MSG_CHANNEL_WINDOW_ADJUST bottleneck
https://bugzilla.mindrot.org/show_bug.cgi?id=3505
Celeste Liu <CoelacanthusHex at gmail.com> changed:
What |Removed |Added
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CC| |CoelacanthusHex at gmail.com
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