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* [Bug remote/26710] New: disable delayed ack on TCP connection for better performance
@ 2020-10-06 15:11 sn2010 at onlinehome dot de
2020-10-08 6:10 ` [Bug remote/26710] " sn2010 at onlinehome dot de
2020-10-08 6:12 ` sn2010 at onlinehome dot de
0 siblings, 2 replies; 3+ messages in thread
From: sn2010 at onlinehome dot de @ 2020-10-06 15:11 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=26710
Bug ID: 26710
Summary: disable delayed ack on TCP connection for better
performance
Product: gdb
Version: HEAD
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: remote
Assignee: unassigned at sourceware dot org
Reporter: sn2010 at onlinehome dot de
Target Milestone: ---
Created attachment 12890
--> https://sourceware.org/bugzilla/attachment.cgi?id=12890&action=edit
wireshark protocol for delayed ack (marked pakets)
When using gdb with tcp remote connection, the host may collect and delay tcp
acknowledgments. Running on Windows10 or a Raspberry with debian stretch, I
could see a 40 ms delay after the target has send a single char '+'. The gdb is
waiting for this char to continue, but the host OS will delay the ack for 40
ms.
On Windows, it could be changed by a registry key TcpAckFrequency:
https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/registry-entry-control-tcp-acknowledgment-behavior
But this is a rough method that affects all TCP connections.
A better solution seems to be to set TCP_QUICKACK (Linux >2.4) or
SIO_TCP_SET_ACK_FREQUENCY (on Windows). This a short discussion about setting
the option:
https://stackoverflow.com/questions/55034112/c-disable-delayed-ack-on-windows
The delayed ack is not the same as the TCP_NODELAY that disables the nagle
algorithm on the sending side, its an optimization on the receiver.
Thanks for reading.
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* [Bug remote/26710] disable delayed ack on TCP connection for better performance
2020-10-06 15:11 [Bug remote/26710] New: disable delayed ack on TCP connection for better performance sn2010 at onlinehome dot de
@ 2020-10-08 6:10 ` sn2010 at onlinehome dot de
2020-10-08 6:12 ` sn2010 at onlinehome dot de
1 sibling, 0 replies; 3+ messages in thread
From: sn2010 at onlinehome dot de @ 2020-10-08 6:10 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=26710
--- Comment #1 from Johannes S. <sn2010 at onlinehome dot de> ---
This issue can be closed.
I have discovered the 'QStartNoAckMode' option in the gdb remote protocol. This
is the solution for this problem at its origin. For a TCP connection, the short
ACK messages can be turned of and the problem with delayed TCP acks is avoided.
Trying to turn off the delayed ack from the sender side is difficult, there are
no portable options and its the matter of the OS to accept changing delayed ack
behaviour or not.
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* [Bug remote/26710] disable delayed ack on TCP connection for better performance
2020-10-06 15:11 [Bug remote/26710] New: disable delayed ack on TCP connection for better performance sn2010 at onlinehome dot de
2020-10-08 6:10 ` [Bug remote/26710] " sn2010 at onlinehome dot de
@ 2020-10-08 6:12 ` sn2010 at onlinehome dot de
1 sibling, 0 replies; 3+ messages in thread
From: sn2010 at onlinehome dot de @ 2020-10-08 6:12 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=26710
Johannes S. <sn2010 at onlinehome dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |NOTABUG
--- Comment #2 from Johannes S. <sn2010 at onlinehome dot de> ---
as explained in the comment above.
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2020-10-06 15:11 [Bug remote/26710] New: disable delayed ack on TCP connection for better performance sn2010 at onlinehome dot de
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2020-10-08 6:12 ` sn2010 at onlinehome dot de
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