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

Minchan Kim
2014-05-29T07:40:47Z

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);
+
current->in_iowait = 1;
schedule();
current->in_iowait = 0;

>
> Cheers,
> Rusty.
>
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--
Kind regards,
Minchan Kim