Bug 498033
| Summary: | "serial8250: too much work for irq4" on HVM Guests | ||||||
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| Product: | Red Hat Enterprise Linux 4 | Reporter: | Qian Cai <qcai> | ||||
| Component: | xen | Assignee: | Markus Armbruster <armbru> | ||||
| Status: | CLOSED DUPLICATE | QA Contact: | Virtualization Bugs <virt-bugs> | ||||
| Severity: | medium | Docs Contact: | |||||
| Priority: | low | ||||||
| Version: | 4.7.z | CC: | clalance, xen-maint | ||||
| Target Milestone: | rc | ||||||
| Target Release: | --- | ||||||
| Hardware: | All | ||||||
| OS: | Linux | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | Bug Fix | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2009-11-24 22:17:55 UTC | Type: | --- | ||||
| Regression: | --- | Mount Type: | --- | ||||
| Documentation: | --- | CRM: | |||||
| Verified Versions: | Category: | --- | |||||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
| Cloudforms Team: | --- | Target Upstream Version: | |||||
| Embargoed: | |||||||
| Bug Depends On: | |||||||
| Bug Blocks: | 458302 | ||||||
| Attachments: |
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Yes, this is a long-standing issue that affects both RHEL-4 and RHEL-5 guests, and probably upstream guests as well (although I haven't tested that specifically). The problem basically comes down to bugs in the qemu emulation for the serial device, but it is *very* complicated to fix, and because it is something that isn't used all that much, it's not something we've put any priority into. Chris Lalancette QEMU's UART emulation does not emulate proper timing at all. Continuous serial I/O can easily overwhelm the guest. Linux detects this, and takes proper action to protect itself. Emulating proper timing looks hard and expensive. A less ambitious fix that could be good enough is sketched here: http://lkml.org/lkml/2008/2/7/485 Just for future reference, this patch has also been trotted around: http://marc.info/?l=linux-serial&m=121863945506976&w=2 Chris Lalancette Oops, this and 501026 are actually dupes. I'm going to close this one as a dup of that, since that other one has had more recent activity. Chris Lalancette *** This bug has been marked as a duplicate of bug 501026 *** |
Created attachment 341589 [details] dmesg with "too much work" messages Description of problem: Lots of messages pop-up in HVM guest. serial8250: too much work for irq4 Version-Release number of selected component (if applicable): kernel-2.6.9-78.0.17.EL How reproducible: always Steps to Reproduce: 1. reserve gs-bl460cg1-01.rhts.bos.redhat.com from RHTS. 2. install RHEL5.2.z Dom0 kernel - 2.6.18-92.1.22.el5 3. install RHEL4.7.z HVM guest. 4. xm create -c rhel4.xml # cat rhel4.xml name = "rhel4u7_x86_64_hvm" uuid = "c4b83c37-0369-9c68-9ba1-9cd9d47a30e5" maxmem = 512 memory = 512 vcpus = 2 builder = "hvm" kernel = "/usr/lib/xen/boot/hvmloader" boot = "c" pae = 1 acpi = 1 apic = 1 localtime = 0 on_poweroff = "destroy" on_reboot = "restart" on_crash = "restart" device_model = "/usr/lib64/xen/bin/qemu-dm" sdl = 0 vnc = 1 vncunused = 1 disk = [ "file:/var/lib/xen/images/rhel4u7_x86_64_hvm.img,hda,w", ",hdc:cdrom,r" ] vif = [ "type=ioemu" ] serial = "pty" Actual results: After login via xm serial console, lots of the above message pop-up. Expected results: No such message.