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Re: [Qemu-devel] [PATCH v6 0/5] Coroutines for better asynchronous progr


From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH v6 0/5] Coroutines for better asynchronous programming
Date: Sat, 16 Jul 2011 13:08:55 +0300

On Mon, Jun 27, 2011 at 12:21 PM, Stefan Hajnoczi <address@hidden> wrote:
> Here is the latest version of the coroutine series with Mac OS X fixes from
> Andreas Färber <address@hidden>.
>
> QEMU is event-driven and suffers when blocking operations are performed 
> because
> VM execution may be stopped until the operation completes.  Therefore many
> operations that could block are performed asynchronously and a callback is
> invoked when the operation has completed.  This allows QEMU to continue
> executing while the operation is pending.
>
> The downside to callbacks is that they split up code into many smaller
> functions, each of which is a single step in a state machine that quickly
> becomes complex and hard to understand.  Callback functions also result in 
> lots
> of noise as variables are packed and unpacked into temporary structs that pass
> state to the callback function.
>
> This patch series introduces coroutines as a solution for writing asynchronous
> code while still having a nice sequential control flow.  The semantics are
> explained in the second patch.  The fourth patch adds automated tests.
>
> A nice feature of coroutines is that it is relatively easy to take synchronous
> code and lift it into a coroutine to make it asynchronous.  Work has been done
> to move qcow2 request processing into coroutines and thereby make it
> asynchronous (today qcow2 will perform synchronous metadata accesses).  This
> qcow2 work is still ongoing and not quite ready for mainline yet.
>
> Coroutines are also being used for virtfs (virtio-9p) so I have submitted this
> patch now because virtfs patches that depend on coroutines are being 
> published.

Coroutines seem to work fine on OpenBSD (Sparc64, also tests are
passed) and mingw32, with a few minor issues.

With simpletrace enabled there is a link failure:
$ make test-coroutine
  LINK  test-coroutine
simpletrace.o: In function `get_clock':
/src/qemu/qemu-timer.h:117: undefined reference to `use_rt_clock'

This can be fixed for example by adding qemu-timer-common.o to the
list of linked objects.

I can't compile coroutine tests for Mingw32 because of this:
$ make test-coroutine
  CC    test-coroutine.o
In file included from
/usr/local/i686-mingw32msvc/include/glib-2.0/glib/galloca.h:30:0,
                 from /usr/local/i686-mingw32msvc/include/glib-2.0/glib.h:30,
                 from /src/qemu/test-coroutine.c:14:
/usr/local/i686-mingw32msvc/include/glib-2.0/glib/gtypes.h:30:24:
fatal error: glibconfig.h: No such file or directory

I used glib win32 zips from
http://ftp.gnome.org/pub/gnome/binaries/win32/glib/2.12/, is there a
better site? Otherwise QEMU builds fine and runs under Wine nicely.

> v6:
>  * Use GThread on Mac OS X, fix from Andreas Färber <address@hidden>
>  * abort(3) if coroutine-ucontext.c fails to create a coroutine
>
> v5:
>  * GThread-based implementation for platforms without makecontext(3) (Aneesh 
> Kumar K.V <address@hidden>)
>  * Switch to gtester test framework
>
> v4:
>  * Windows Fibers support (Paolo Bonzini <address@hidden>)
>  * Return-after-setjmp() fix (Aneesh Kumar K.V <address@hidden>)
>  * Re-entrancy for multi-threaded coroutines support
>  * qemu-coroutine.h cleanup and documentation
>
> v3:
>  * Updated LGPL v2 license header to use web link
>  * Removed atexit(3) pool freeing
>  * Removed thread-local current/leader
>  * Documented thread-safety limitation
>  * Disabled trace events
>
> v2:
>  * Added ./check-coroutine --lifecycle-benchmark for performance measurement
>  * Split pooling into a separate patch with performance justification
>  * Set maximum pool size to prevent holding onto too many free coroutines
>  * Added atexit(3) handler to free pool
>  * Coding style cleanups
>
> Aneesh Kumar K.V (1):
>  coroutine: implement coroutines using gthread
>
> Anthony Liguori (1):
>  Add hard build dependency on glib
>
> Kevin Wolf (1):
>  coroutine: introduce coroutines
>
> Stefan Hajnoczi (2):
>  coroutine: add test-coroutine automated tests
>  coroutine: add test-coroutine --benchmark-lifecycle
>
>  .gitignore           |    1 +
>  Makefile             |    5 +-
>  Makefile.objs        |   13 +++
>  Makefile.target      |    1 +
>  configure            |   31 +++++++
>  coroutine-gthread.c  |  131 ++++++++++++++++++++++++++++
>  coroutine-ucontext.c |  230 
> ++++++++++++++++++++++++++++++++++++++++++++++++++
>  coroutine-win32.c    |   92 ++++++++++++++++++++
>  qemu-coroutine-int.h |   48 +++++++++++
>  qemu-coroutine.c     |   75 ++++++++++++++++
>  qemu-coroutine.h     |   95 +++++++++++++++++++++
>  test-coroutine.c     |  192 +++++++++++++++++++++++++++++++++++++++++
>  trace-events         |    5 +
>  13 files changed, 918 insertions(+), 1 deletions(-)
>  create mode 100644 coroutine-gthread.c
>  create mode 100644 coroutine-ucontext.c
>  create mode 100644 coroutine-win32.c
>  create mode 100644 qemu-coroutine-int.h
>  create mode 100644 qemu-coroutine.c
>  create mode 100644 qemu-coroutine.h
>  create mode 100644 test-coroutine.c
>
> --
> 1.7.5.4
>
>
>



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