On Thu, Jan 24, 2013 at 11:34:59AM +0100, Ivo Sieben wrote: > The "normal" spin lock that guards the N_TTY line discipline read section > is replaced by a raw spin lock. > > On a PREEMP_RT system this prevents unwanted scheduling overhead when data is > read at the same time as data is being received: while RX IRQ threaded handling > is busy a TTY read call is performed from a RT priority > threaded IRQ priority. > The read call tries to take the read section spin lock (held by the threaded > IRQ) which blocks and causes a context switch to/from the threaded IRQ handler > until the spin lock is unlocked. > > On a 240 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling > overhead on the TTY read call. Out of how many us total? And this really makes a difference? I'd like to hear the rt developers opinoin of this. > Signed-off-by: Ivo Sieben <meltedpianoman@xxxxxxxxx Forgot the trailing '>' :) thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
