On Fri, Sep 27, 2013 at 07:20:21AM +0200, Stefan Weil wrote:
> Am 11.09.2013 16:42, schrieb Stefan Hajnoczi:
> > The 'gthread' coroutine backend was written before the freelist (aka
> > pool) existed in qemu-coroutine.c.
> >
> > This means that every thread is expected to exit when its coroutine
> > terminates. It is not possible to reuse threads from a pool.
> >
> > This patch automatically disables the pool when 'gthread' is used. This
> > allows the 'gthread' backend to work again (for example,
> > tests/test-coroutine completes successfully instead of hanging).
> >
> > I considered implementing thread reuse but I don't want quirks like CPU
> > affinity differences due to coroutine threads being recycled. The
> > 'gthread' backend is a reference backend and it's therefore okay to skip
> > the pool optimization.
> >
> > Note this patch also makes it easy to toggle the pool for benchmarking
> > purposes:
> >
> > ./configure --with-coroutine-backend=ucontext \
> > --disable-coroutine-pool
> >
> > Reported-by: Gabriel Kerneis <gabr...@kerneis.info>
> > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > ---
> > configure | 24 ++++++++++++++++++++++++
> > qemu-coroutine.c | 34 +++++++++++++++++++---------------
> > 2 files changed, 43 insertions(+), 15 deletions(-)
> >
>
> This patch is important for QEMU 1.5 as well, but needs some
> modifications there.
> A recent bug report for MinGW shows that the win32 coroutine needs it, too.
coroutine-win32.c is designed to support reuse:
static void CALLBACK coroutine_trampoline(void *co_)
{
Coroutine *co = co_;
while (true) {
co->entry(co->entry_arg);
qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
}
}
We return from qemu_coroutine_switch() when the fiber is reused and
simply run another iteration of the while loop.
Why do you say win32 coroutines should disable the pool?
Stefan
