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From: Olivier Matz <olivier.matz@6wind.com>
To: Phil Yang <Phil.Yang@arm.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"drc@linux.vnet.ibm.com" <drc@linux.vnet.ibm.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	Ruifeng Wang <Ruifeng.Wang@arm.com>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v2] mbuf: use C11 atomics for refcnt operations
Date: Wed, 8 Jul 2020 13:43:02 +0200
Message-ID: <20200708114301.GN5869@platinum> (raw)
In-Reply-To: <VE1PR08MB4640935CA367E216F788DEE5E9670@VE1PR08MB4640.eurprd08.prod.outlook.com>

On Wed, Jul 08, 2020 at 04:48:33AM +0000, Phil Yang wrote:
> > -----Original Message-----
> > From: Stephen Hemminger <stephen@networkplumber.org>
> > Sent: Wednesday, July 8, 2020 1:13 AM
> > To: Phil Yang <Phil.Yang@arm.com>
> > Cc: david.marchand@redhat.com; dev@dpdk.org; drc@linux.vnet.ibm.com;
> > Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>;
> > olivier.matz@6wind.com; Ruifeng Wang <Ruifeng.Wang@arm.com>; nd
> > <nd@arm.com>
> > Subject: Re: [dpdk-dev] [PATCH v2] mbuf: use C11 atomics for refcnt
> > operations
> > 
> > On Tue,  7 Jul 2020 18:10:33 +0800
> > Phil Yang <phil.yang@arm.com> wrote:
> > 
> > > +	return (uint16_t)(__atomic_add_fetch((int16_t *)&shinfo-
> > >refcnt_atomic,
> > > +
> > 
> > Why do you need so many casts here?
> > The type of refcnt_atomic is now uint16 after your patch.
> 
> In the existing code, the input parameter type for this API is signed integer. For example:
> drivers/net/netvsc/hn_rxtx.c:531
> lib/librte_mbuf/rte_mbuf.h:1194
> 
> However, the output type of rte_mbuf_ext_refcnt related APIs is not uniform. We use these typecast to consistent with the current API definition.

Would it make sense to cast the increment instead?

I mean:

	return __atomic_add_fetch(&m->refcnt, (uint16_t)value, __ATOMIC_ACQ_REL);

instead of:

	return (uint16_t)(__atomic_add_fetch((int16_t *)&m->refcnt, value,
				__ATOMIC_ACQ_REL));


The same could apply to __rte_pktmbuf_pinned_extbuf_decref() I think:

> -	if (likely(rte_atomic16_add_return
> -			(&shinfo->refcnt_atomic, -1)))
> +	if (likely(__atomic_add_fetch((int *)&shinfo->refcnt_atomic, -1,
> +				     __ATOMIC_ACQ_REL)))

By the way, why was the cast was to (int *) in this case? I think
it can overwrite fields beside refcnt.

  reply	other threads:[~2020-07-08 11:43 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-11 10:26 [dpdk-dev] [PATCH] mbuf: use c11 " Phil Yang
2020-07-03 15:38 ` David Marchand
2020-07-06  8:03   ` Phil Yang
2020-07-07 10:10 ` [dpdk-dev] [PATCH v2] mbuf: use C11 " Phil Yang
2020-07-07 17:13   ` Stephen Hemminger
2020-07-08  4:48     ` Phil Yang
2020-07-08 11:43       ` Olivier Matz [this message]
2020-07-09  9:52         ` Phil Yang
2020-07-08  5:11   ` Phil Yang
2020-07-08 11:44   ` Olivier Matz
2020-07-09 10:00     ` Phil Yang
2020-07-09 10:10   ` [dpdk-dev] [PATCH v3] mbuf: use C11 atomic built-ins " Phil Yang
2020-07-09 11:03     ` Olivier Matz
2020-07-09 13:00       ` Phil Yang
2020-07-09 13:31         ` Honnappa Nagarahalli
2020-07-09 14:10           ` Phil Yang
2020-07-09 15:58     ` [dpdk-dev] [PATCH v4 1/2] " Phil Yang
2020-07-09 15:58       ` [dpdk-dev] [PATCH v4 2/2] doc: announce deprecation of refcnt atomic member Phil Yang
2020-07-10  2:55         ` Ruifeng Wang
2020-07-13 15:54           ` Phil Yang
2020-07-14 10:41         ` Ananyev, Konstantin
2020-07-15 12:29       ` [dpdk-dev] [PATCH v4 1/2] mbuf: use C11 atomic built-ins for refcnt operations David Marchand
2020-07-15 12:49         ` Aaron Conole
2020-07-15 16:29         ` Phil Yang
2020-07-16  4:16         ` Phil Yang
2020-07-16 11:30           ` David Marchand
2020-07-16 13:20             ` Dodji Seketeli
2020-07-16 19:11               ` David Marchand
2020-07-17  4:41                 ` Phil Yang
2020-07-16 11:32       ` Olivier Matz
2020-07-17  4:36       ` [dpdk-dev] [PATCH v5 1/2] mbuf: use C11 atomic builtins " Phil Yang
2020-07-17  4:36         ` [dpdk-dev] [PATCH v5 2/2] doc: announce deprecation of refcnt atomic member Phil Yang
2020-07-17 11:45           ` Olivier Matz
2020-07-17 14:32           ` David Marchand
2020-07-17 14:35             ` David Marchand
2020-07-17 16:06               ` Ananyev, Konstantin
2020-07-17 16:20               ` Bruce Richardson
2020-07-21  8:35                 ` David Marchand
2020-07-21  8:48                   ` Ananyev, Konstantin
2020-07-21  8:37         ` [dpdk-dev] [PATCH v5 1/2] mbuf: use C11 atomic builtins for refcnt operations David Marchand

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