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From: Gavin Hu <Gavin.Hu@arm.com>
To: Stephen Hemminger <stephen@networkplumber.org>,
	Joyce Kong <Joyce.Kong@arm.com>
Cc: "maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>,
	"tiwei.bie@intel.com" <tiwei.bie@intel.com>,
	"zhihong.wang@intel.com" <zhihong.wang@intel.com>,
	"thomas@monjalon.net" <thomas@monjalon.net>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	"yinan.wang@intel.com" <yinan.wang@intel.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	nd <nd@arm.com>, "dev@dpdk.org" <dev@dpdk.org>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v2 1/2] virtio: one way barrier for split vring used idx
Date: Fri, 3 Apr 2020 08:55:38 +0000	[thread overview]
Message-ID: <VI1PR08MB5376C462FA810AD92556C4518FC70@VI1PR08MB5376.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20200402084756.2dc243ae@hermes.lan>

Hi Stephen, 

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Thursday, April 2, 2020 11:48 PM
> To: Joyce Kong <Joyce.Kong@arm.com>
> Cc: maxime.coquelin@redhat.com; tiwei.bie@intel.com;
> zhihong.wang@intel.com; thomas@monjalon.net; jerinj@marvell.com;
> yinan.wang@intel.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Gavin Hu <Gavin.Hu@arm.com>; nd
> <nd@arm.com>; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2 1/2] virtio: one way barrier for split vring
> used idx
> 
> On Thu,  2 Apr 2020 10:57:52 +0800
> Joyce Kong <joyce.kong@arm.com> wrote:
> 
> > -					(vq)->vq_used_cons_idx))
> > +static inline uint16_t
> > +virtqueue_nused(struct virtqueue *vq)
> vq is unmodified and should be const
> 
> > +{
> > +	uint16_t idx;
> > +	if (vq->hw->weak_barriers) {
> Put blank line between declaration and if statement
Will fix in v3.
> 
> > +/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports
> > + * a slightly better perf, which comes from the saved branch by the
> compiler.
> > + * The if and else branches are identical with the smp and cio barriers
> both
> > + * defined as compiler barriers on x86.
> > + */
> 
> Do not put comments on left margin (except in function prolog).
Will fix in v3.
> 
> > +#ifdef RTE_ARCH_X86_64
> > +		idx = vq->vq_split.ring.used->idx;
> > +		rte_smp_rmb();
> > +#else
> > +		idx = __atomic_load_n(&(vq)->vq_split.ring.used->idx,
> > +				__ATOMIC_ACQUIRE);
> > +#endif
> > +	} else {
> > +		idx = vq->vq_split.ring.used->idx;
> > +		rte_cio_rmb();
> > +	}
> > +	return (idx - vq->vq_used_cons_idx);
> 
> Parenthesis around arguments to return are unnecessary.
> BSD code likes it, Linux style does not.
Will fix in v3.
> 
> > +}
> 
> This kind of arch specific code is hard to maintain.
> Does it really make that much difference.
Yes, a stronger than required barrier is a performance killer, especially in the fast path.
The test was conducted on the ThunderX2+Intel XL710 testbed, the PVP test case.
/Gavin

  reply	other threads:[~2020-04-03  8:55 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12  9:24 [dpdk-dev] [PATCH v1 0/2] one way barrier for split vring idx Joyce Kong
2020-02-12  9:24 ` [dpdk-dev] [PATCH v1 1/2] virtio: one way barrier for split vring used idx Joyce Kong
2020-02-12  9:24 ` [dpdk-dev] [PATCH v1 2/2] virtio: one way barrier for split vring avail idx Joyce Kong
2020-04-02  2:57 ` [dpdk-dev] [PATCH v2 0/2] one way barrier for split vring idx Joyce Kong
2020-04-02  2:57 ` [dpdk-dev] [PATCH v2 1/2] virtio: one way barrier for split vring used idx Joyce Kong
2020-04-02 15:47   ` Stephen Hemminger
2020-04-03  8:55     ` Gavin Hu [this message]
2020-04-16  4:40       ` Honnappa Nagarahalli
2020-04-16  6:46         ` Joyce Kong
2020-04-02  2:57 ` [dpdk-dev] [PATCH v2 2/2] virtio: one way barrier for split vring avail idx Joyce Kong
2020-04-06 15:26 ` [dpdk-dev] [PATCH v3 0/2] one way barrier for split vring idx Joyce Kong
2020-04-16  9:08   ` Ye Xiaolong
2020-04-06 15:26 ` [dpdk-dev] [PATCH v3 1/2] virtio: one way barrier for split vring used idx Joyce Kong
2020-04-17  6:51   ` Ye Xiaolong
2020-04-17  8:14     ` Joyce Kong
2020-04-06 15:26 ` [dpdk-dev] [PATCH v3 2/2] virtio: one way barrier for split vring avail idx Joyce Kong
2020-04-24  3:39 ` [dpdk-dev] [PATCH v4 0/2] one way barrier for split vring idx Joyce Kong
2020-04-28 16:06   ` Maxime Coquelin
2020-04-29 17:45   ` Ferruh Yigit
2020-04-30  9:09     ` Maxime Coquelin
2020-04-30  9:16       ` Joyce Kong
2020-04-30  9:24         ` Maxime Coquelin
2020-04-24  3:39 ` [dpdk-dev] [PATCH v4 1/2] virtio: one way barrier for split vring used idx Joyce Kong
2020-04-27  9:03   ` Maxime Coquelin
2020-04-24  3:39 ` [dpdk-dev] [PATCH v4 2/2] virtio: one way barrier for split vring avail idx Joyce Kong
2020-04-27  9:03   ` Maxime Coquelin
2020-04-30  9:14 ` [dpdk-dev] [PATCH v5 0/2] one way barrier for split vring idx Joyce Kong
2020-04-30 20:54   ` Maxime Coquelin
2020-04-30  9:14 ` [dpdk-dev] [PATCH v5 1/2] virtio: one way barrier for split vring used idx Joyce Kong
2020-04-30 22:58   ` Ferruh Yigit
2020-05-04 10:04     ` Maxime Coquelin
2020-04-30  9:14 ` [dpdk-dev] [PATCH v5 2/2] virtio: one way barrier for split vring avail idx Joyce Kong

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