From: Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>
To: Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>,
Andrew Boyer <andrew.boyer@amd.com>,
"dev@dpdk.org" <dev@dpdk.org>
Cc: Neel Patel <neel.patel@amd.com>, nd <nd@arm.com>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
nd <nd@arm.com>
Subject: RE: [PATCH 2/3] net/ionic: remove duplicate barriers
Date: Tue, 20 Feb 2024 02:02:08 +0000 [thread overview]
Message-ID: <AM0PR08MB50731F0F22A0CF5B35BA8B699F502@AM0PR08MB5073.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <AM0PR08MB50736C38BA5048CCCF1B5FDA9F512@AM0PR08MB5073.eurprd08.prod.outlook.com>
> -----Original Message-----
> From: Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>
> Sent: Monday, February 19, 2024 4:17 PM
> To: Andrew Boyer <andrew.boyer@amd.com>; dev@dpdk.org
> Cc: Neel Patel <neel.patel@amd.com>; nd <nd@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH 2/3] net/ionic: remove duplicate barriers
>
> Hi Andrew,
>
> I think that this barrier may have been added to ensure any writes to q-
> >hw_index and q->head_idx complete before ionic_q_flush computes val.
> Dependency chains can also prevent reordering if that's the case this barrier is
> not required.
> However, I have the following concern.
>
> > diff --git a/drivers/net/ionic/ionic_main.c
> > b/drivers/net/ionic/ionic_main.c index 1f24f64a33..814bb3b8f4 100644
> > --- a/drivers/net/ionic/ionic_main.c
> > +++ b/drivers/net/ionic/ionic_main.c
> > @@ -223,7 +223,6 @@ ionic_adminq_post(struct ionic_lif *lif, struct
> > ionic_admin_ctx *ctx)
> > q->head_idx = Q_NEXT_TO_POST(q, 1);
> >
> > /* Ring doorbell */
> > - rte_wmb();
> > ionic_q_flush(q);
> >
> > err_out:
>
> Ionic_q_flush(q) uses q->hw_index and q->head_idx to compute the value of
> val which it writes to the address stored in q->db. I can see that q->head_idx is
> updated before the removed rte_wmb(), therefore it's safe to assume that " q-
> >head_idx = Q_NEXT_TO_POST(q, 1)" and "val = IONIC_DBELL_QID(q-
> >hw_index) | q->head_idx" will maintain the program order due to that
> dependency. But I don't know if there exists a dependency chain over q-
> >hw_index. If not, then that may have been the motive behind this barrier.
>
Since q->hw_index is also updated in the same CPU ionic_q_flush will
always see the correct value, consequently val should be always correct.
It's safe to remove this barrier.
> > diff --git a/drivers/net/ionic/ionic_rxtx_sg.c
> > b/drivers/net/ionic/ionic_rxtx_sg.c
> > index e8dec99c04..3820fd850f 100644
> > --- a/drivers/net/ionic/ionic_rxtx_sg.c
> > +++ b/drivers/net/ionic/ionic_rxtx_sg.c
> > @@ -218,7 +218,6 @@ ionic_xmit_pkts_sg(void *tx_queue, struct
> rte_mbuf
> > **tx_pkts,
> > }
> >
> > if (nb_tx > 0) {
> > - rte_wmb();
> > ionic_txq_flush(q);
> >
> > txq->last_wdog_cycles = rte_get_timer_cycles(); diff --git
> > a/drivers/net/ionic/ionic_rxtx_simple.c
> > b/drivers/net/ionic/ionic_rxtx_simple.c
> > index 9674b4d1df..4c9b9415ad 100644
> > --- a/drivers/net/ionic/ionic_rxtx_simple.c
> > +++ b/drivers/net/ionic/ionic_rxtx_simple.c
> > @@ -191,7 +191,6 @@ ionic_xmit_pkts(void *tx_queue, struct rte_mbuf
> > **tx_pkts,
> > }
> >
> > if (nb_tx > 0) {
> > - rte_wmb();
> > ionic_txq_flush(q);
> >
> > txq->last_wdog_cycles = rte_get_timer_cycles();
> > --
> > 2.17.1
next prev parent reply other threads:[~2024-02-20 2:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-16 17:07 [PATCH 0/3] net/ionic, common/ionic: add vdev support Andrew Boyer
2024-02-16 17:07 ` [PATCH 1/3] common/ionic: create common code library for ionic Andrew Boyer
2024-02-16 17:07 ` [PATCH 2/3] net/ionic: remove duplicate barriers Andrew Boyer
2024-02-19 22:16 ` Wathsala Wathawana Vithanage
2024-02-20 2:02 ` Wathsala Wathawana Vithanage [this message]
2024-02-20 18:31 ` Boyer, Andrew
2024-02-16 17:07 ` [PATCH 3/3] net/ionic: add vdev support for embedded applications Andrew Boyer
2024-02-19 15:24 ` Ferruh Yigit
2024-02-19 22:02 ` Boyer, Andrew
2024-02-20 2:02 ` Honnappa Nagarahalli
2024-02-21 1:16 ` Boyer, Andrew
2024-02-20 8:28 ` Ferruh Yigit
2024-02-20 14:39 ` Honnappa Nagarahalli
2024-02-16 19:39 ` [PATCH 0/3] net/ionic, common/ionic: add vdev support Ferruh Yigit
2024-02-20 20:42 ` [PATCH v2 " Andrew Boyer
2024-02-20 20:42 ` [PATCH v2 1/3] common/ionic: create common code library for ionic Andrew Boyer
2024-02-20 20:42 ` [PATCH v2 2/3] net/ionic: remove duplicate barriers Andrew Boyer
2024-02-20 20:42 ` [PATCH v2 3/3] net/ionic: add vdev support for embedded applications Andrew Boyer
2024-02-23 1:52 ` Honnappa Nagarahalli
2024-02-21 16:36 ` [PATCH v2 0/3] net/ionic, common/ionic: add vdev support Ferruh Yigit
2024-02-23 13:48 ` Ferruh Yigit
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