From: Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>
To: 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: Mon, 19 Feb 2024 22:16:34 +0000 [thread overview]
Message-ID: <AM0PR08MB50736C38BA5048CCCF1B5FDA9F512@AM0PR08MB5073.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20240216170704.55523-3-andrew.boyer@amd.com>
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.
> 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:[~2024-02-19 22:16 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 [this message]
2024-02-20 2:02 ` Wathsala Wathawana Vithanage
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=AM0PR08MB50736C38BA5048CCCF1B5FDA9F512@AM0PR08MB5073.eurprd08.prod.outlook.com \
--to=wathsala.vithanage@arm.com \
--cc=Honnappa.Nagarahalli@arm.com \
--cc=andrew.boyer@amd.com \
--cc=dev@dpdk.org \
--cc=nd@arm.com \
--cc=neel.patel@amd.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).