[Qemu-devel] [Bug 1481272] Re: main-loop: WARNING: I/O thread spun for 1000 iterations

[Sibiao Luo <luosibiao@huawei.com>]

Good catch, thanks stefanha for your kindly reminds with such good tools
(git-bisect) to determine which commit caused this problem. I'm very
sorry that i did not try it as your instruction timely, mainly that i
focus on the openstack(nova&cinder) currently in the new company and
have to adapt to the new work flow & role as quickly as possible.
According to me trying that 05e514b1d4d5bd4209e2c8bbc76ff05c85a235f3 is
the first bad commit pushed by pbonzini.

My trying results as following:
master             074a992 Merge remote-tracking branch 'remotes/cody/tags/block-pull-request' into staging <---> latest version fail
qemu-2.3-stable dfa83a6 Update version for 2.3.1 release                                                                  <---> qemu-2.3-stable good

[root@PEK1000012301 qemu]# git bisect start
[root@PEK1000012301 qemu]# git bisect bad 074a992
[root@PEK1000012301 qemu]# git bisect good dfa83a6
Bisecting: a merge base must be tested
[e5b3a24181ea0cebf1c5b20f44d016311b7048f0] Update version for v2.3.0 release
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 1105 revisions left to test after this (roughly 10 steps)
[afa25c4bb5bd0732dca4aa0691fd4682d242925f] Merge remote-tracking branch 'remotes/kraxel/tags/pull-sdl-20150611-1' into staging
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 552 revisions left to test after this (roughly 9 steps)
[922f893e57da24bc80db3e79bea56485d1c111fa] ahci: assert is_ncq for process_ncq
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 274 revisions left to test after this (roughly 8 steps)
[711dc6f36b74fe65a6e5a1847f1152717d887f8a] Merge remote-tracking branch 'remotes/cody/tags/jtc-for-upstream-pull-request' into staging
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 138 revisions left to test after this (roughly 7 steps)
[226d007dbd75ec8d0f12d0f9e1ce66caf55d49e4] gdbstub: Set current CPU on interruptions
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect bad
Bisecting: 67 revisions left to test after this (roughly 6 steps)
[b9c46307996856d03ddc1527468ff5401ac03a79] Merge remote-tracking branch 'remotes/mdroth/tags/qga-pull-2015-07-21-tag' into staging
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 32 revisions left to test after this (roughly 5 steps)
[f793d97e454a56d17e404004867985622ca1a63b] Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect bad
Bisecting: 17 revisions left to test after this (roughly 4 steps)
[80adb8fcad4778376a11d394a9e01516819e2327] tcg/aarch64: use 32-bit offset for 32-bit softmmu emulation
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect bad
Bisecting: 8 revisions left to test after this (roughly 3 steps)
[dc94bd9166af5236a56bd5bb06845911915a925c] Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect bad
Bisecting: 3 revisions left to test after this (roughly 2 steps)
[6493c975af75be5b8d9ade954239bdf5492b7911] aio-win32: reorganize polling loop
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 1 revision left to test after this (roughly 1 step)
[21a03d17f2edb1e63f7137d97ba355cc6f19d79f] AioContext: fix broken placement of event_notifier_test_and_clear
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect good
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[05e514b1d4d5bd4209e2c8bbc76ff05c85a235f3] AioContext: optimize clearing the EventNotifier
<<<compile QEMU with this branch and try to launch VM to test as comment#0>>>

[root@PEK1000012301 qemu]# git bisect bad
05e514b1d4d5bd4209e2c8bbc76ff05c85a235f3 is the first bad commit
commit 05e514b1d4d5bd4209e2c8bbc76ff05c85a235f3
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Tue Jul 21 16:07:53 2015 +0200

    AioContext: optimize clearing the EventNotifier
    
    It is pretty rare for aio_notify to actually set the EventNotifier.  It
    can happen with worker threads such as thread-pool.c's, but otherwise it
    should never be set thanks to the ctx->notify_me optimization.  The
    previous patch, unfortunately, added an unconditional call to
    event_notifier_test_and_clear; now add a userspace fast path that
    avoids the call.
    
    Note that it is not possible to do the same with event_notifier_set;
    it would break, as proved (again) by the included formal model.
    
    This patch survived over 3000 reboots on aarch64 KVM.
    
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Reviewed-by: Fam Zheng <famz@redhat.com>
    Tested-by: Richard W.M. Jones <rjones@redhat.com>
    Message-id: 1437487673-23740-7-git-send-email-pbonzini@redhat.com
    Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

:100644 100644 5c8b266c72b79e07f881a563da189e0267937766 d4770336c5d5355758c3da207b8be5160f66fc5f M    aio-posix.c
:100644 100644 7afc9992d682d335b4fce58182b580f7f678f503 50a68674589aa3c6418604bfb9320e915f624796 M    aio-win32.c
:100644 100644 d625e8a8035656711f156078bbc7784b4f4754b0 9a98a74acb99bbf74c004ab2de0d09ca78eac84c M    async.c
:040000 040000 6f98147da6fdc258f6b7b967ee90d02686311951 11705f58169772ff280c44f4f7d7e7c367600f1a M    docs
:040000 040000 97f8f766a2ad81d2a262f0379643c3ebaa9d32bc 49b13585c2fad748b6f7c7cb49944dc6c2a149f8 M    include

Best Regards & Thx,
Sibiao Luo

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https://bugs.launchpad.net/bugs/1481272

Title:
  main-loop: WARNING: I/O thread spun for 1000 iterations

Status in QEMU:
  New

Bug description:
  I compile the latest qemu to launch a VM but the monitor output the
  "main-loop: WARNING: I/O thread spun for 1000 iterations".

  # /usr/local/bin/qemu-system-x86_64 -name rhel6 -S -no-kvm -m 1024M -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid c9dd2a5c-40f2-fd3d-3c54-9cd84f8b9174 -rtc base=utc  -drive file=/home/samba-share/ubuntu.img,if=none,id=drive-virtio-disk0,format=qcow2,cache=none -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=disk,serial=425618d4-871f-4021-bc5d-bcd7f1b5ca9c,bootindex=0 -vnc :1 -boot menu=on -monitor stdio
  QEMU 2.3.93 monitor - type 'help' for more information
  (qemu) c
  (qemu) main-loop: WARNING: I/O thread spun for 1000 iterations               <-----------------------

  qemu]# git branch -v
  * master               e95edef Merge remote-tracking branch 'remotes/sstabellini/tags/xen-migration-2.4-tag' into staging

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