Messages in this thread | | | Date | Fri, 03 May 2013 19:02:46 +0400 | From | Stas Sergeev <> | Subject | Regression: ftdi_sio is slow (since Wed Oct 10 15:05:06 2012) |
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Hi.
We have a regression because of this patch: http://lkml.indiana.edu/hypermail/linux/kernel/1210.1/01456.html While it is arguably reasonable to have this for tcdrain or close, it also slows down poll/select a lot because n_tty_poll() does this:
tty_chars_in_buffer(tty) < WAKEUP_CHARS
And it also slows down TIOCOUTQ ioctl I think (not measured). The slowdown of select() is big, the customer reports the inability to work that way.
Is this patch really needed? I mean, if the time to check TEMT is longer than to xmit that char, then what's the use? Or, if it is really a big deal, I guess it would be necessary to add a separate, .chars_in_buffer_fast method.
Thoughts?
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