On Fri, 2008-08-15 at 10:08 +0800, Liu Yu wrote: > > -----Original Message----- > > From: Christian Ehrhardt [mailto:ehrhardt@xxxxxxxxxxxxxxxxxx] > > Sent: Wednesday, August 13, 2008 8:47 PM > > To: Liu Yu > > Cc: kvm-ppc@xxxxxxxxxxxxxxx > > Subject: Re: Serial stdio overwhelming interrupts > > > > Liu Yu wrote: > > > Hi guys, > > > > > > In my kvm machine, I use serial as its default stdio. > > > But when display a number of characters, e.g. cat a big ascii file, > > > the serial always hangs as encount overwhelming interrupts, > > and then output a kernel log "serial8250: too much work for irq 42". > > > > > > I found that the serial in qemu is primitive so that it > > generate a interrupt on every single character. > > > This make it easier to reach the threshold of reporting > > "too much work". > > > > > > I had to use the patch below to get this issue walked arroud. > > > > > > Have you guys ever met the serial hanging problem before? > > > > > > > We had that some times in the beginning while we brought up > > interrupts. > > But since that time it did never occur again and I thought we > > fixed it. > > Maybe your use case of catting a file to it is stressing it > > now to a new extend triggering it again. > > > > I found this. > http://www.archivum.info/qemu-devel@xxxxxxxxxx/2008-02/msg00169.html > I don’t know how it is going now. Because I still work on the branch kvm-70rc1 of qemu > Maybe it has been solved. AFAIK it has not been solved, and neither Linux nor qemu developers plan to change their behavior. In the URL above, a kernel developer suggests changing qemu's behavior. The problem is that the Linux driver reads serial data in a loop but gives up after a fixed number (256) of iterations. I'm not sure why the kernel does that, since I think interrupts are enabled while that happens. As a workaround you could use telnet or ssh to cat your large files. You're welcome to reopen the discussion on the LKML and KVM lists. -- Hollis Blanchard IBM Linux Technology Center -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
