At Xilinx we have started to run our fork of QEMU on Windows and are
starting to distrubute this to customers. As part of this QEMU is
launched from an Eclipse based GUI on Windows hosts. This uncovered a
few performance issues in QEMU when running on CPU restricted machines.

What we see is that when QEMU is run on a machine where there aren't
enough spare CPUs on the host, QEMU is extreamly slow. We especially see
this when running our multi-architecture QEMU setup (MicroBlaze and ARM)
because we are running two QEMU instances as well as what else is
running on the machine.

Generally two instances of QEMU will never reach a Linux login prompt
when run on four host CPUs, but will reach the login prompt when run on
eight CPUs.

We investigated the issue and realised that it is mostly because QEMU
did not block and instead the IO thread just busy looped. This basically
locked up two CPUs (two QEMU instances) with IO threads not leaving
enough resources on the machine.

This patch series fixed the issue for us on our fork of QEMU. Our fork
is based on QEMU 2.8.1 and does not include MTTCG support. I have not
tested this on the mainline QEMU or with MTTCG. It is on my todo list to
see if I can repdouce the same issue on Windows with mainline QEMU. In
the meantime I wanted to send this series to see if anyone else has seen
Windows performance issues and if this helps with the problems. In order
to see the issue we had to do a full Linux boot, smaller baremetal
applications generally don't reproduce the same issue.

Also, most of these patches are editing the QEMU implementation of Glib,
obviously these fixes (if applicable) will need to be ported to Glib and
applied there as well. I just wanted to start here.

Alistair Francis (4):
  util/aio-win32: Only select on what we are actually waiting for
  util/oslib-win32: Remove invalid check
  util/oslib-win32: Fix up if conditional
  util/oslib-win32: Recursivly pass the timeout

 util/aio-win32.c   | 13 ++++++++++---
 util/oslib-win32.c | 25 +++++++++++++++++++------
 2 files changed, 29 insertions(+), 9 deletions(-)

-- 
2.11.0

Hi,

This series failed automatic build test. Please find the testing commands and
their output below. If you have docker installed, you can probably reproduce it
locally.

Subject: [Qemu-devel] [RFC v1 0/4]  Windows runtime improvements
Message-id: cover.1498607452.git.alistair.francis@xilinx.com
Type: series

=== TEST SCRIPT BEGIN ===
#!/bin/bash
set -e
git submodule update --init dtc
# Let docker tests dump environment info
export SHOW_ENV=1
export J=8
time make docker-test-quick@centos6
time make docker-test-build@min-glib
time make docker-test-mingw@fedora
=== TEST SCRIPT END ===

Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
fatal: Cannot update paths and switch to branch 'test' at the same time.
Did you intend to checkout 'origin/patchew/cover.1498607452.git.alistair.francis@xilinx.com' which can not be resolved as commit?
Traceback (most recent call last):
  File "/home/fam/bin/patchew", line 440, in test_one
    git_clone_repo(clone, r["repo"], r["head"], logf)
  File "/home/fam/bin/patchew", line 53, in git_clone_repo
    cwd=clone)
  File "/usr/lib64/python3.5/subprocess.py", line 271, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['git', 'checkout', 'origin/patchew/cover.1498607452.git.alistair.francis@xilinx.com', '-b', 'test']' returned non-zero exit status 128



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On Thu, 07/06 16:48, no-reply@patchew.org wrote:
> Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
> fatal: Cannot update paths and switch to branch 'test' at the same time.
> Did you intend to checkout 'origin/patchew/cover.1498607452.git.alistair.francis@xilinx.com' which can not be resolved as commit?
> Traceback (most recent call last):
>   File "/home/fam/bin/patchew", line 440, in test_one
>     git_clone_repo(clone, r["repo"], r["head"], logf)
>   File "/home/fam/bin/patchew", line 53, in git_clone_repo
>     cwd=clone)
>   File "/usr/lib64/python3.5/subprocess.py", line 271, in check_call
>     raise CalledProcessError(retcode, cmd)
> subprocess.CalledProcessError: Command '['git', 'checkout', 'origin/patchew/cover.1498607452.git.alistair.francis@xilinx.com', '-b', 'test']' returned non-zero exit status 128

Ignore this please, patchew is recovering from a bad state.