Bug 498033 - "serial8250: too much work for irq4" on HVM Guests
"serial8250: too much work for irq4" on HVM Guests
Status: CLOSED DUPLICATE of bug 501026
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: xen (Show other bugs)
All Linux
low Severity medium
: rc
: ---
Assigned To: Markus Armbruster
Virtualization Bugs
Depends On:
Blocks: 458302
  Show dependency treegraph
Reported: 2009-04-28 11:26 EDT by CAI Qian
Modified: 2009-12-14 16:28 EST (History)
2 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2009-11-24 17:17:55 EST
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
dmesg with "too much work" messages (14.33 KB, text/plain)
2009-04-28 11:26 EDT, CAI Qian
no flags Details

  None (edit)
Description CAI Qian 2009-04-28 11:26:46 EDT
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):

How reproducible:

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.
Comment 1 Chris Lalancette 2009-04-28 17:47:14 EDT
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
Comment 2 Markus Armbruster 2009-05-22 03:18:29 EDT
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
Comment 3 Chris Lalancette 2009-06-25 09:20:06 EDT
Just for future reference, this patch has also been trotted around:


Chris Lalancette
Comment 4 Chris Lalancette 2009-11-24 17:17:55 EST
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 ***

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