<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> </head> <body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"> <br> <div><br> <blockquote type="cite"> <div>On Feb 19, 2024, at 9:02 PM, Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com> wrote:</div> <br class="Apple-interchange-newline"> <div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> -----Original Message-----<br> From: Wathsala Wathawana Vithanage <<a href="mailto:wathsala.vithanage@arm.com">wathsala.vithanage@arm.com</a>><br> Sent: Monday, February 19, 2024 4:17 PM<br> To: Andrew Boyer <<a href="mailto:andrew.boyer@amd.com">andrew.boyer@amd.com</a>>;<span class="Apple-converted-space"> </span><a href="mailto:dev@dpdk.org">dev@dpdk.org</a><br> Cc: Neel Patel <<a href="mailto:neel.patel@amd.com">neel.patel@amd.com</a>>; nd <<a href="mailto:nd@arm.com">nd@arm.com</a>>; Honnappa<br> Nagarahalli <<a href="mailto:Honnappa.Nagarahalli@arm.com">Honnappa.Nagarahalli@arm.com</a>>; nd <<a href="mailto:nd@arm.com">nd@arm.com</a>><br> Subject: RE: [PATCH 2/3] net/ionic: remove duplicate barriers<br> <br> Hi Andrew,<br> <br> I think that this barrier may have been added to ensure any writes to q-<br> <blockquote type="cite">hw_index and q->head_idx complete before ionic_q_flush computes val.<br> </blockquote> Dependency chains can also prevent reordering if that's the case this barrier is<br> not required.<br> However, I have the following concern.<br> <br> <blockquote type="cite">diff --git a/drivers/net/ionic/ionic_main.c<br> b/drivers/net/ionic/ionic_main.c index 1f24f64a33..814bb3b8f4 100644<br> --- a/drivers/net/ionic/ionic_main.c<br> +++ b/drivers/net/ionic/ionic_main.c<br> @@ -223,7 +223,6 @@ ionic_adminq_post(struct ionic_lif *lif, struct<br> ionic_admin_ctx *ctx)<br> q->head_idx = Q_NEXT_TO_POST(q, 1);<br> <br> /* Ring doorbell */<br> - rte_wmb();<br> ionic_q_flush(q);<br> <br> err_out:<br> </blockquote> <br> Ionic_q_flush(q) uses q->hw_index and q->head_idx to compute the value of<br> val which it writes to the address stored in q->db. I can see that q->head_idx is<br> updated before the removed rte_wmb(), therefore it's safe to assume that " q-<br> <blockquote type="cite">head_idx = Q_NEXT_TO_POST(q, 1)" and "val = IONIC_DBELL_QID(q-<br> hw_index) | q->head_idx" will maintain the program order due to that<br> </blockquote> dependency. But I don't know if there exists a dependency chain over q-<br> <blockquote type="cite">hw_index. If not, then that may have been the motive behind this barrier.<br> </blockquote> <br> </blockquote> <br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Since q->hw_index is also updated in the same CPU ionic_q_flush will</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">always see the correct value, consequently val should be always correct.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">It's safe to remove this barrier.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"> <br> </div> </blockquote> </div> <br> <div>Thank you for the careful review. We agree with this analysis.</div> <div><br> </div> <div>-Andrew</div> <div><br> </div> </body> </html>