If I run this and print out test-pattern afterwards, I get

test-pattern

((485 0 11) (1024 0 11) (1024 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0
11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1
0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11)
(1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1023 0 11) (1024 0 11)
(1024 0 11) (1024 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11) (1 0 11)
(1 0 11) (1 0 11) (1 0 11) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0
10) (1 0 10) (1023 0 10) (1024 0 10) (1024 0 10) (1024 0 10) (1 0 10)
(1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0
10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1
0 10) (1 0 10) (1 0 10) (1023 0 10) (1024 0 10) (1024 0 10) (1024 0
10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1
0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10)
(1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1 0 10) (1023 0 10)

[...]

(1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0
8) (1 0 8) (1 0 8) (1 0 8) (1023 0 8) (1024 0 8) (1024 0 8) (1024 0 8)
(1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0
8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 8) (1 0 7) (1
0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7)
(1023 0 7) (1024 0 7) (1024 0 7) (1024 0 7) (1 0 7) (1 0 7) (1 0 7) (1
0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7)
(1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0
7) (1 0 7) (1 0 7) (1 0 7) (1023 0 7) (1024 0 7) (1024 0 7) (1024 0 7)
(1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0
7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1 0 7) (1

[...]

0 6) (1 0 6) (1 0 6) (1 0 6) (1023 0 6) (1024 0 6) (1024 0 6) (1024 0
6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1
0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6)
(1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0
6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1
0 6) (1023 0 6) (1024 0 6) (1024 0 6) (1024 0 6) (1 0 6) (1 0 6) (1 0
6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1 0 6) (1

And from then on (actually backwards in time) only packets with single
characters, with perhaps 100 filter calls per second.

Which in itself is not too hot a speed, but gets awful in consequence
because the filter routine gets only called for single characters.

I don't know _what_ Emacs does do the pipe/pty that causes only single
characters to gather/be processed, with a sporadic 1024 packet getting
through from time to time, but I hate it.  Some setting must be on the
pipe that causes the writer to stall before further writes in many
cases until Emacs has read the next character.  And after some time
the pipe gets filled properly now and then, with single characters in
between.

I don't get it.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum