Re: [dpdk-dev] [PATCH v5 3/3] eal/stack: enable lock-free stack for aarch64

["Phil Yang (Arm Technology China)" <Phil.Yang@arm.com>]

> -----Original Message-----
> From: Eads, Gage <gage.eads@intel.com>
> Sent: Monday, July 22, 2019 10:35 PM
> To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>; dev@dpdk.org
> Cc: thomas@monjalon.net; jerinj@marvell.com; hemant.agrawal@nxp.com;
> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm
> Technology China) <Gavin.Hu@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v5 3/3] eal/stack: enable lock-free stack for aarch64
> 
> > diff --git a/lib/librte_stack/rte_stack_lf_stubs.h
> > b/lib/librte_stack/rte_stack_lf_stubs.h
> > new file mode 100644
> > index 0000000..d924bc6
> > --- /dev/null
> > +++ b/lib/librte_stack/rte_stack_lf_stubs.h
> > @@ -0,0 +1,59 @@
> > +/* SPDX-License-Identifier: BSD-3-Clause
> > + * Copyright(c) 2019 Arm Limited
> > + */
> > +
> > +#ifndef _RTE_STACK_LF_STUBS_H_
> > +#define _RTE_STACK_LF_STUBS_H_
> > +
> > +#include <rte_common.h>
> > +#include <rte_atomic.h>
> > +
> > +static __rte_always_inline unsigned int __rte_stack_lf_count(struct
> > +rte_stack *s) {
> > +	/* stack_lf_push() and stack_lf_pop() do not update the list's
> > contents
> > +	 * and stack_lf->len atomically, which can cause the list to appear
> > +	 * shorter than it actually is if this function is called while other
> > +	 * threads are modifying the list.
> > +	 *
> > +	 * However, given the inherently approximate nature of the
> > get_count
> > +	 * callback -- even if the list and its size were updated atomically,
> > +	 * the size could change between when get_count executes and
> > when the
> > +	 * value is returned to the caller -- this is acceptable.
> > +	 *
> > +	 * The stack_lf->len updates are placed such that the list may appear
> > to
> > +	 * have fewer elements than it does, but will never appear to have
> > more
> > +	 * elements. If the mempool is near-empty to the point that this is a
> > +	 * concern, the user should consider increasing the mempool size.
> > +	 */
> > +	return (unsigned int)rte_atomic64_read((rte_atomic64_t *)
> > +			&s->stack_lf.used.len);
> > +}
> 
> Since the stub functions are not functional, these comments should be
> removed and the function simply return 0. The rte_atomic.h include can be
> removed as well.

OK. Will do it. Thanks.