Commit Graph

8 Commits

Author SHA1 Message Date
Linus Torvalds
f23eb2b2b2 tty: stop using "delayed_work" in the tty layer
Using delayed-work for tty flip buffers ends up causing us to wait for
the next tick to complete some actions.  That's usually not all that
noticeable, but for certain latency-critical workloads it ends up being
totally unacceptable.

As an extreme case of this, passing a token back-and-forth over a pty
will take two ticks per iteration, so even just a thousand iterations
will take 8 seconds assuming a common 250Hz configuration.

Avoiding the whole delayed work issue brings that ping-pong test-case
down to 0.009s on my machine.

In more practical terms, this latency has been a performance problem for
things like dive computer simulators (simulating the serial interface
using the ptys) and for other environments (Alan mentions a CP/M emulator).

Reported-by: Jef Driesen <jefdriesen@telenet.be>
Acked-by: Greg KH <gregkh@suse.de>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 16:17:32 -07:00
Linus Torvalds
f74b944419 Merge branch 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl
* 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl:
  BKL: That's all, folks
  fs/locks.c: Remove stale FIXME left over from BKL conversion
  ipx: remove the BKL
  appletalk: remove the BKL
  x25: remove the BKL
  ufs: remove the BKL
  hpfs: remove the BKL
  drivers: remove extraneous includes of smp_lock.h
  tracing: don't trace the BKL
  adfs: remove the big kernel lock
2011-03-16 17:21:00 -07:00
Arnd Bergmann
5edc341313 drivers: remove extraneous includes of smp_lock.h
These were missed the last time I cleaned this up
globally, because of code moving around or new code
getting merged.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2011-03-02 00:02:40 +01:00
Tejun Heo
0a1f1a0b62 tty_ldisc: don't use flush_scheduled_work()
flush_scheduled_work() is scheduled to be deprecated.  Explicitly sync
flush the used work items instead.  Note that before this change,
flush_scheduled_work() wouldn't have properly flushed tty->buf.work if
it were on timer.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-02-03 14:12:25 -08:00
Jiri Slaby
7f90cfc505 TTY: ldisc, fix open flag handling
When a concrete ldisc open fails in tty_ldisc_open, we forget to clear
TTY_LDISC_OPEN. This causes a false warning on the next ldisc open:
WARNING: at drivers/char/tty_ldisc.c:445 tty_ldisc_open+0x26/0x38()
Hardware name: System Product Name
Modules linked in: ...
Pid: 5251, comm: a.out Tainted: G        W  2.6.32-5-686 #1
Call Trace:
 [<c1030321>] ? warn_slowpath_common+0x5e/0x8a
 [<c1030357>] ? warn_slowpath_null+0xa/0xc
 [<c119311c>] ? tty_ldisc_open+0x26/0x38
 [<c11936c5>] ? tty_set_ldisc+0x218/0x304
...

So clear the bit when failing...

Introduced in c65c9bc3ef (tty: rewrite the ldisc locking) back in
2.6.31-rc1.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Reported-by: Sergey Lapin <slapin@ossfans.org>
Tested-by: Sergey Lapin <slapin@ossfans.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-29 14:51:54 -08:00
Philippe Rétornaz
1c95ba1e1d tty_ldisc: Fix BUG() on hangup
A kernel BUG when bluetooth rfcomm connection drop while the associated
serial port is open is sometime triggered.

It seems that the line discipline can disappear between the
tty_ldisc_put and tty_ldisc_get. This patch fall back to the N_TTY line
discipline if the previous discipline is not available anymore.

Signed-off-by: Philippe Retornaz <philippe.retornaz@epfl.ch>
Acked-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-09 15:05:50 -08:00
Jiri Slaby
100eeae2c5 TTY: restore tty_ldisc_wait_idle
It was removed in 65b770468e (tty-ldisc: turn ldisc user count into
a proper refcount), but we need to wait for last user to quit the
ldisc before we close it in tty_set_ldisc.

Otherwise weird things start to happen. There might be processes
waiting in tty_read->n_tty_read on tty->read_wait for input to appear
and at that moment, a change of ldisc is fatal. n_tty_close is called,
it frees read_buf and the waiting process is still in the middle of
reading and goes nuts after it is woken.

Previously we prevented close to happen when others are in ldisc ops
by tty_ldisc_wait_idle in tty_set_ldisc. But the commit above removed
that. So revoke the change and test whether there is 1 user (=we), and
allow the close then.

We can do that without ldisc/tty locks, because nobody else can open
the device due to TTY_LDISC_CHANGING bit set, so we in fact wait for
everybody to leave.

I don't understand why tty_ldisc_lock would be needed either when the
counter is an atomic variable, so this is a lockless
tty_ldisc_wait_idle.

On the other hand, if we fail to wait (timeout or signal), we have to
reenable the halted ldiscs, so we take ldisc lock and reuse the setup
path at the end of tty_set_ldisc.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Sebastian Andrzej Siewior <bigeasy@breakpoint.cc>
LKML-Reference: <20101031104136.GA511@Chamillionaire.breakpoint.cc>
LKML-Reference: <1287669539-22644-1-git-send-email-jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Cc: stable@kernel.org [32, 33, 36]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-09 15:04:21 -08:00
Greg Kroah-Hartman
96fd7ce58f TTY: create drivers/tty and move the tty core files there
The tty code should be in its own subdirectory and not in the char
driver with all of the cruft that is currently there.

Based on work done by Arnd Bergmann <arnd@arndb.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-05 08:10:33 -07:00