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Re: [Qemu-devel] [PATCH v6 0/5] Coroutines for better asynchronous progr
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v6 0/5] Coroutines for better asynchronous programming |
Date: |
Mon, 18 Jul 2011 14:09:19 +0100 |
On Sat, Jul 16, 2011 at 11:08 AM, Blue Swirl <address@hidden> wrote:
> 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.
Do you want me to send a patch to add qemu-timer-common.o or is this
easy to do while merging?
> 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.
Paolo, Stefan Weil: Any ideas regarding w32 glib headers above?
Stefan