Re: Remote asynchronous processes

[Michael Albinus]

Michael Albinus <address@hidden> writes:

Hi,

> On the Tramp ML, there is a discussion about performance of remote
> asynchronous processes. start-file-process / make-process take too much
> time to finish.
>
> One of the reasons is, that Tramp opens first a shell on the remote
> host, performs sanity checks, and runs the command after that. Well, I
> cannot change this in general; the sanity checks have been added due to
> feedback from users.
>
> One idea to change the situation is, to remove all sanity checks from
> make-process. That is, if a user has a default directory
> "/ssh:user@host:/path/to/dir", and if he calls
>
> (make-process
>  :name "test"
>  :buffer (current-buffer)
>  :command '("cmd")
>  :file-handler t))
>
> this is translated directly into
>
> ssh -l user -o ControlMaster=auto -o ControlPath='tramp.%C' \
>   -o ControlPersist=no host "cd /path/to/dir; cmd"
>
> This would improve performance significantly. The drawback is, that
> Tramp does not perform convenience checks, like password handling.

I have played with this idea, and the output is the appended file
tramp-make-process.el. It changes the make-process implementation of
Tramp for all methods defined in tramp-sh.el (like "ssh") and
tramp-adb.el.

This is a proof-of-concept, and shouldn't be used for production. Read
the commentary in the file for limitations.

However, the speed optimization is remarkable. I've tested it with the
following code snippet:

--8<---------------cut here---------------start------------->8---
(let ((tramp-verbose 0)
      (default-directory "/ssh::/"))
  ;; Fill the caches.
  (start-file-process "" nil "true")
  ;; Run benchmark.
  (benchmark-run 10
    (start-file-process "" nil "true")))
--8<---------------cut here---------------end--------------->8---

In the default case, the result is

--8<---------------cut here---------------start------------->8---
(3.623666842 80 1.183512312)
--8<---------------cut here---------------end--------------->8---

If tramp-make-process.el is loaded, the result is

--8<---------------cut here---------------start------------->8---
(0.022762177 0 0.0)
--8<---------------cut here---------------end--------------->8---

Similar results, if I use "/adb::/" as default directory:

--8<---------------cut here---------------start------------->8---
(4.599374061 2 0.03429497299999973)
--8<---------------cut here---------------end--------------->8---

vs

--8<---------------cut here---------------start------------->8---
(0.013003183 0 0.0)
--8<---------------cut here---------------end--------------->8---

Comments?

Best regards, Michael.

tramp-make-process.el
Description: Text document