Re: [PATCH v2 0/9] mostly lockless tty echo

[Greg Kroah-Hartman]

On Sat, Jun 15, 2013 at 10:04:20AM -0400, Peter Hurley wrote:
> ** v2 changes **
> - Rebased on v2 of 'lockless tty flip buffers'
> 
> This 3rd of 4 patchsets implements a mostly-lockless tty echo output.
> 
> Because echoing is performed solely by the single-threaded ldisc
> receive_buf() method, most of the lockless requirements are already
> in-place. The main existing complications were;
> 1) Echoing could overrun itself. A fixed-size buffer is used to record
>    the operations necessary when outputting the echoes; the most recent
>    echo data is preserved.
> 2) An attempt to push unprocessed echoes is made by the n_tty_write method
>    (on a different thread) before attempting write output.
> 
> The overrun condition is solved by outputting the echoes in blocks and
> ensuring that at least that much space is available each time an echo
> operation is committed. At the conclusion of each flip buffer received,
> any remaining unprocessed echoes are output.
> 
> This block output method is particularly effective when there is no reader
> (the tty is output-only) and termios is misconfigured with echo enabled.
> 
> The concurrent access by the n_tty_write() method is already excluded
> by the existing output_lock mutex.

Applied, thanks.

greg k-h
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