On Fri, Apr 25, 2014 at 02:29:37PM +0100, Will Deacon wrote: > Hi all, > > On Thu, Apr 17, 2014 at 12:36:09PM +0100, Will Deacon wrote: > > When running on a hideously slow system (~10Mhz FPGA) with a bunch of
Hey, still faster then the 4.77 MHz 8088 chips I started with :-) > > debug printk invocations on the timer interrupt path, we end up filling > > the log buffer faster than we can drain it. > > > > The reason is that console_unlock (which is responsible for moving > > messages out of logbuf to hand over to the console driver) removes one > > message at a time, briefly re-enabling interrupts between each of them. > > If the interrupt path prints more than a single message, then we can > > easily generate more messages than we can print for a regular, recurring > > interrupt (e.g. a 1khz timer). This results in messages getting silently > > dropped, leading to counter-intuitive, incomplete printk traces on the > > console. > > > > Rather than run the console_unlock loop with interrupts disabled (which > > has obvious latency problems), this patch records the sequence number of > > the last message in the log buffer after taking the logbuf_lock. We can > > then print this fixed amount of work before re-enabling interrupts again, > > making sure we keep up with ourself. Other CPUs could still potentially > > flood the buffer, but there's little that we can do to protect against > > that. > > Any thoughts on these two patches? I can understand the reluctance to make > changes to printk, but I had a horrible time debugging timers without these > patches! They look fine to me. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
