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I am debugging a very slow performance of git commands over SSH, including via packages such as VC and Magit.

Even using VC on emacs -Q is extremely slow.

I get

Tramp: Opening connection git for <<hostname>> using ssh

over and over, when I would expect TRAMP to reuse the first connection.

What is strange is that this behavior seems to be confined to git commands: if I open eshell and run ls, TRAMP opens a new connection only once (and the following commands runs quite fast). In this case, the output is (attention to nil instead of git):

Tramp: Opening connection nil for <<hostname>> using ssh

Conversely, if I do git status, every time the command is run, a new connection is opened, with the text mentioned above.

Would someone know how to make TRAMP reuse the connection even for git commands?

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  • eshell implements its own ls command in elisp, so I think that's not a good comparison. which ls => "eshell/ls is a byte-compiled Lisp function in ‘em-ls.el’."
    – phils
    Commented Mar 9 at 1:31
  • Maybe research/check your ControlMaster config for ssh. That's the "normal" approach I'm familiar with for getting ssh to re-use its connections. For a while now Tramp has tried to make use of that by default, but it may depend on which Tramp method you're using, and/or how ssh is configured on your system.
    – phils
    Commented Mar 9 at 1:36

1 Answer 1

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In vc, vc-git-command is called, which uses vc-do-command. This uses an asynchronous process via start-file-process, and so does Tramp: opening a new process for a given git command.

I haven't checked for magit, but something similar might happen.

You might try to improve the performance by using direct async processes in Tramp (see its manual).

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