Re: [dpdk-dev] [PATCH v1 2/2] ring: use wfe to wait for ring tail update on aarch64

[Gavin Hu <Gavin.Hu@arm.com>]

Hi Honnappa,

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Friday, April 24, 2020 10:46 PM
> To: Gavin Hu <Gavin.Hu@arm.com>; dev@dpdk.org
> Cc: nd <nd@arm.com>; david.marchand@redhat.com;
> thomas@monjalon.net; jerinj@marvell.com; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Phil Yang <Phil.Yang@arm.com>; Joyce Kong
> <Joyce.Kong@arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v1 2/2] ring: use wfe to wait for ring tail update on
> aarch64
> 
> <snip>
> 
> Hi Gavin,
> 	There are other sync modes added to rte_ring library. Can you
> please extend this to other rte_pause() calls in the library?
I looked into the other two calls to rte_cause, they can't use the rte_wait_until_equal_XX APIs simply.
Maybe new APIs are required? 
Here is the 32-bit API for your reference:
rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected, int memorder)
> 
> Thanks,
> Honnappa
> 
> > Subject: [PATCH v1 2/2] ring: use wfe to wait for ring tail update on
> aarch64
> >
> > Instead of polling for tail to be updated, use wfe instruction.
> >
> > Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Steve Capper <steve.capper@arm.com>
> > Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > ---
> >  lib/librte_ring/rte_ring_c11_mem.h | 4 ++--
> > lib/librte_ring/rte_ring_generic.h | 3 +--
> >  2 files changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/lib/librte_ring/rte_ring_c11_mem.h
> > b/lib/librte_ring/rte_ring_c11_mem.h
> > index 0fb73a337..764d8f186 100644
> > --- a/lib/librte_ring/rte_ring_c11_mem.h
> > +++ b/lib/librte_ring/rte_ring_c11_mem.h
> > @@ -2,6 +2,7 @@
> >   *
> >   * Copyright (c) 2017,2018 HXT-semitech Corporation.
> >   * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
> > + * Copyright (c) 2019 Arm Limited
> >   * All rights reserved.
> >   * Derived from FreeBSD's bufring.h
> >   * Used as BSD-3 Licensed with permission from Kip Macy.
> > @@ -21,8 +22,7 @@ update_tail(struct rte_ring_headtail *ht, uint32_t
> > old_val, uint32_t new_val,
> >  	 * we need to wait for them to complete
> >  	 */
> >  	if (!single)
> > -		while (unlikely(ht->tail != old_val))
> > -			rte_pause();
> > +		rte_wait_until_equal_relaxed_32(&ht->tail, old_val);
> >
> >  	__atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);  } diff --
> > git a/lib/librte_ring/rte_ring_generic.h b/lib/librte_ring/rte_ring_generic.h
> > index 953cdbbd5..682852783 100644
> > --- a/lib/librte_ring/rte_ring_generic.h
> > +++ b/lib/librte_ring/rte_ring_generic.h
> > @@ -23,8 +23,7 @@ update_tail(struct rte_ring_headtail *ht, uint32_t
> > old_val, uint32_t new_val,
> >  	 * we need to wait for them to complete
> >  	 */
> >  	if (!single)
> > -		while (unlikely(ht->tail != old_val))
> > -			rte_pause();
> > +		rte_wait_until_equal_relaxed_32(&ht->tail, old_val);
> >
> >  	ht->tail = new_val;
> >  }
> > --
> > 2.17.1