Re: virtio ring cleanups, which save stack on older gcc

Dave Chinner
2014-05-29T10:39:29Z

On Thu, May 29, 2014 at 04:41:17PM +0900, Minchan Kim wrote:
> Hello Rusty,
>
> On Thu, May 29, 2014 at 04:56:41PM +0930, Rusty Russell wrote:
> > They don't make much difference: the easier fix is use gcc 4.8
> > which drops stack required across virtio block's virtio_queue_rq
> > down to that kmalloc in virtio_ring from 528 to 392 bytes.
> >
> > Still, these (*lightly tested*) patches reduce to 432 bytes,
> > even for gcc 4.6.4. Posted here FYI.
>
> I am testing with below which was hack for Dave's idea so don't have
> a machine to test your patches until tomorrow.
> So, I will queue your patches into testing machine tomorrow morning.
>
> Thanks!
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f5c6635b806c..95f169e85dbe 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4241,10 +4241,13 @@ EXPORT_SYMBOL_GPL(yield_to);
> void __sched io_schedule(void)
> {
> struct rq *rq = raw_rq();
> + struct blk_plug *plug = current->plug;
>
> delayacct_blkio_start();
> atomic_inc(&rq->nr_iowait);
> - blk_flush_plug(current);
> + if (plug)
> + blk_flush_plug_list(plug, true);
> +

Could simply be

- blk_flush_plug(current);
+ blk_schedule_flush_plug(current);

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com