On Tue, 1 Apr 2014 13:37:00 +0200 Jiri Slaby <jslaby@xxxxxxx> wrote: > The 8250 driver now reports many of these: > serial8250: too much work for irq4 > These messages turned out to be common these days with a use of > virtualization. I tried to increase the limit of processed characters > in commit e7328ae1848966181a7ac47e8ae6cddbd2cf55f3 (serial: 8250, > increase PASS_LIMIT) in 2011. It was raised from 256 to 512, but it is > still not enough, apparently. A lot of emulations model the queue completely incorrectly. However simply hiding it with a pr_debug is the wrong answer - it wants fixing. If we set a large PASS_LIMIT then it's not going to be a big loss on real hardware - we'll burp for a second or two and continue, but it ought to cure the virtualisation case. If it doesn't we've got a bigger problem because it means we are jammed in the kernel spinning in an IRQ handler feeding data to a fake serial port that never stops being an IRQ and we end up hanging the virtualised OS for a long period If that is happening then we need to actually workaround whatever crapware emulator is triggering it so we don't hang the guest for long periods if there is a big I/O. If its a real port that is jammed our normal time around the loop on the LPC bus is going to be a shade over 24uS (32uS if TX is jammed on) So we certainly ought to be able to go a bit higher without major crisis. Beyond that if it is still tripping then instead of whining we need to set IIR_NO_INT and set a polling timer to turn the IRQ back on next timer tick. That way a crappy emulated port can't hang the guest with a continual stream of data and a busted real one might actually sort out. Alan -- 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
