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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: |
Thu, 12 Jul 2018 09:23:49 -0000 |
I tested Pavel's patch, applying it to master
(c447afd5783b9237fa51b7a85777007d8d568bfc), but I'm afraid it only made
things worse - qemu has now been booting the test kernel for 30 minutes
but the boot has still not completed. The last console messages printed
were:
piix 0000:00:01.1: not 100% native mode: will probe irqs later
ide0: BM-DMA at 0xc100-0xc107
ide1: BM-DMA at 0xc108-0xc10f
Running strace -p on the qemu process shows it calling ppoll once per
second:
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
ppoll([{fd=0, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN},
{fd=10, events=POLLIN}, {fd=11, events=POLLIN}], 5, {tv_sec=1, tv_nsec=0},
NULL, 8) = 0 (Timeout)
--
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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.
To manage notifications about this bug go to:
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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, 2018/07/08
- [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 <=
- [Qemu-devel] [Bug 1774677] Re: -icount increases boot time by >10x, Pavel Dovgalyuk, 2018/07/12