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* re your change to the low_latency flag in the hso driver in 2.6.29-rc1
@ 2009-01-12 17:23 Denis Joseph Barrow
       [not found] ` <496B7CA9.6080403-x9gZzRpC1QbQT0dZR+AlfA@public.gmane.org>
  0 siblings, 1 reply; 2+ messages in thread
From: Denis Joseph Barrow @ 2009-01-12 17:23 UTC (permalink / raw)
  To: Alan Cox
  Cc: Linux USB kernel mailing list, Linux netdev Mailing list,
	Paul Hardwick

Hi Alan,
I remember removing the low_latency flag to 0 once & if I recall correctly performance 
was severely impacted & there may have been other problems which I don't recall.
even worse I believe the code can now hang the kernel, the fix is simple, in
put_rxbuf_data I'm dependent on the TTY_THROTTLED bit to exit the loop.
Now tty_insert_flip_string can return 0 bytes leading to an infinite loop if tty buffers are full,
as write_length_remaining never goes to zero as I am dependent on the line
discipline being called from tty_flip_buffer_push to set TTY_THROTTLED by calling flush_to_ldisc
checking if curr_write_len=0 from tty_insert_flip_string might fix the problem
Please look at put_rxbuf_data carefully, there might be other gremlins. The serial port
is supposed to be high performance this fix will impact this

-- 
best regards,
D.J. Barrow

Linux Kernel Developer
Option NV, Gaston Geenslaan 14, 3001 Leuven, Belgium
 
T: +32 16 311 621
F: +32 16 207 164
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^ permalink raw reply	[flat|nested] 2+ messages in thread

• [parent not found: <496B7CA9.6080403-x9gZzRpC1QbQT0dZR+AlfA@public.gmane.org>]

• • * Re: re your change to the low_latency flag in the hso driver in 2.6.29-rc1
           [not found] ` <496B7CA9.6080403-x9gZzRpC1QbQT0dZR+AlfA@public.gmane.org>
    @ 2009-01-12 17:45   ` Alan Cox
      0 siblings, 0 replies; 2+ messages in thread
    From: Alan Cox @ 2009-01-12 17:45 UTC (permalink / raw)
      To: Denis Joseph Barrow
      Cc: Linux USB kernel mailing list, Linux netdev Mailing list,
    	Paul Hardwick
    
    > I remember removing the low_latency flag to 0 once & if I recall correctly performance 
    > was severely impacted & there may have been other problems which I don't recall.
    
    The modern buffering and old buffering are rather different so that
    shouldn't be a problem.
    
    > Now tty_insert_flip_string can return 0 bytes leading to an infinite loop if tty buffers are full,
    > as write_length_remaining never goes to zero as I am dependent on the line
    > discipline being called from tty_flip_buffer_push to set TTY_THROTTLED by calling flush_to_ldisc
    
    In all cases tty_insert_flip_string may return 0 for other reasons (eg
    out of memory).
    
    > checking if curr_write_len=0 from tty_insert_flip_string might fix the problem
    > Please look at put_rxbuf_data carefully, there might be other gremlins. The serial port
    > is supposed to be high performance this fix will impact this
    
    Will do, but it should have no impact at all on throughput - in fact it
    ought to improve it. You can't call tty_flip_buffer_push() from an
    IRQ handler with tty->low_latency set anyway...
    
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    ^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2009-01-12 17:45 UTC | newest]

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2009-01-12 17:23 re your change to the low_latency flag in the hso driver in 2.6.29-rc1 Denis Joseph Barrow
     [not found] ` <496B7CA9.6080403-x9gZzRpC1QbQT0dZR+AlfA@public.gmane.org>
2009-01-12 17:45   ` Alan Cox

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