On Fri, 03/13 09:13, Paolo Bonzini wrote:
>
>
> On 13/03/2015 02:38, Fam Zheng wrote:
> > That if the dbs' owner is an iothread, dma should be resumed on the right
> > thread. In this case it is the AioContext of the block device.
> >
> > Signed-off-by: Fam Zheng <f...@redhat.com>
> > ---
> > dma-helpers.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/dma-helpers.c b/dma-helpers.c
> > index 6918572..84f61a7 100644
> > --- a/dma-helpers.c
> > +++ b/dma-helpers.c
> > @@ -95,8 +95,10 @@ static void reschedule_dma(void *opaque)
> > static void continue_after_map_failure(void *opaque)
> > {
> > DMAAIOCB *dbs = (DMAAIOCB *)opaque;
> > + AioContext *ctx;
> >
> > - dbs->bh = qemu_bh_new(reschedule_dma, dbs);
> > + ctx = blk_get_aio_context(dbs->blk);
> > + dbs->bh = aio_bh_new(ctx, reschedule_dma, dbs);
> > qemu_bh_schedule(dbs->bh);
> > }
> >
> >
>
> This looks good. However, I wonder if dma_aio_cancel should also call
> cpu_unregister_map_client. In this case, it's much better to just use a
> lock for the list (though you can still use atomics for the in-use flag).
The other possibility is grab a reference for the cpu_register_map_client call,
and release it in reschedule_dma. This way the atomics can keep, but we'll need
a "finished" flag in DMAAIOCB to avoid double completion.
Fam
