Re: [Qemu-devel] [PATCH] coroutine: switch per-thread free pool to a global pool

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Dec 5, 2011 at 5:20 PM, Avi Kivity <avi@redhat.com> wrote:
> ucontext-based coroutines use a free pool to reduce allocations and
> deallocations of coroutine objects.  The pool is per-thread, presumably
> to improve locality.  However, as coroutines are usually allocated in
> a vcpu thread and freed in the I/O thread, the pool accounting gets
> screwed up and we end allocating and freeing a coroutine for every I/O
> request.  This is expensive since large objects are allocated via the
> kernel, and are not cached by the C runtime.
>
> Fix by switching to a global pool.  This is safe since we're protected
> by the global mutex.

Looks good to me.  I did check how hw/9pfs/ uses coroutines because it
bounces them into worker threads that are not under the QEMU mutex but
they are not created/destroyed there so we should be okay.

Stefan