Re: [PATCH 1/2] Use kfifo to buffer USB generic serial writes

[Alan Cox]

> The first part of patch uses the kfifo infrastructure to implement a write
> FIFO that accurately returns the amount of space available in the buffer. The
> second makes a minor change to kfifo_put() and __kfifo_put() to add the "const"
> attribute to their input buffer pointers.

Nice, fixes the bug, uses the proper infrastructure and comes out as
loads less code and far easier to read


> +	/* TODO: Much of the time there won't be a write pending and won't be
> +	 * any data ahead of the current chunk. In those cases, we could save
> +	 * a copy by putting the data directly into the URB transfer buffer.
> +	 * This adds some complexity, is it worth it for serial I/O? */
> +	count = kfifo_put(port->write_fifo, buf, count);

If your device has a single transmit URB and isn't doing 2-3MBit the
answer will be no - its in cache anyway and the real hit will be the
writeout for the USB controller to DMA it.


> +		spin_lock_irqsave(&port->write_fifo_lock, flags);
> +		chars = __kfifo_len(port->write_fifo);
> +		spin_unlock_irqrestore(&port->write_fifo_lock, flags);

Any reason for not using kfifo_len() ?

Alan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/