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[Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x
From: |
Andreas Gustafsson |
Subject: |
[Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x |
Date: |
Sun, 08 Jul 2018 12:51:58 -0000 |
I bisected this using the following test case (after the setup shown in
the original bug report, and replacing "e1000" by "ne2k_pci" in the run-
emulator.sh script to avoid a panic in the e1000 driver with some qemu
versions):
QEMU_EXTRA="-icount shift=3,sleep=off" sh run-emulator.sh
The bisection identified the following commit:
281b2201e4e18d5b9a26e1e8d81b62b5581a13be is the first bad commit
commit 281b2201e4e18d5b9a26e1e8d81b62b5581a13be
Author: Pavel Dovgalyuk <address@hidden>
Date: Thu Mar 10 14:56:03 2016 +0300
icount: remove obsolete warp call
qemu_clock_warp call in qemu_tcg_wait_io_event function is not needed
anymore, because it is called in every iteration of main_loop_wait.
Reviewed-by: Paolo Bonzini <address@hidden>
Signed-off-by: Pavel Dovgalyuk <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
With revision 281b2201e4e18d5b9a26e1e8d81b62b5581a13be, the test case
takes 141 seconds to boot. With the previous revision,
33577b47c64435fcc2a1bc01c7e82534256f1fc3, it takes 1.7 seconds.
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https://bugs.launchpad.net/bugs/1774677
Title:
-icount increases boot time by >10x
Status in QEMU:
Confirmed
Bug description:
When I specify the -icount option, some guest operations such as
booting a Linux kernel take more than 10 times longer than otherwise.
For example, the following will boot Aboriginal Linux to the login
prompt about 6 seconds on my system (using TCG, not KVM):
wget
http://landley.net/aboriginal/downloads/old/binaries/1.4.5/system-image-i686.tar.gz
gunzip <system-image-i686.tar.gz | tar xfv -
cd system-image-i686
sh run-emulator.sh
If I replace the last line with
QEMU_EXTRA="-icount shift=auto" sh run-emulator.sh
booting to the login prompt takes about 1 minute 20 seconds.
I have tried different values for "shift" other than the "auto" used
above, but have not been able to find one that gives reasonable
performance. Specifying "sleep=off" also did not help.
During the slow boots, qemu appears to spend most of its time
sleeping, not using the host CPU.
I see this with multiple versions of qemu, including current git
sources (c181ddaa176856b3cd2dfd12bbcf25fa9c884a97), and on multiple
host OSes, including Debian 9 on x86_64.
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- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Peter Maydell, 2018/07/06
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Peter Maydell, 2018/07/06
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Peter Maydell, 2018/07/06
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Andreas Gustafsson, 2018/07/06
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x,
Andreas Gustafsson <=
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Pavel Dovgalyuk, 2018/07/09
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Paolo Bonzini, 2018/07/09
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Pavel Dovgalyuk, 2018/07/09
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Andreas Gustafsson, 2018/07/12
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Pavel Dovgalyuk, 2018/07/12