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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id x5-20020a170902a38500b001e2bfd40b86sm16275326pla.47.2024.04.26.15.57.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Apr 2024 15:57:13 -0700 (PDT) Date: Fri, 26 Apr 2024 15:57:11 -0700 From: Stephen Hemminger <stephen@networkplumber.org> To: Morten =?UTF-8?B?QnLDuHJ1cA==?= <mb@smartsharesystems.com> Cc: "Ferruh Yigit" <ferruh.yigit@amd.com>, "Thomas Monjalon" <thomas@monjalon.net>, "Andrew Rybchenko" <andrew.rybchenko@oktetlabs.ru>, <dev@dpdk.org>, <stable@dpdk.org>, Mattias =?UTF-8?B?UsO2bm5ibG9t?= <mattias.ronnblom@ericsson.com> Subject: Re: [PATCH] ethdev: document that stats reset APIs are not thread-safe Message-ID: <20240426155711.368c0755@hermes.local> In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F3FA@smartserver.smartshare.dk> References: <20240425165308.1078454-1-ferruh.yigit@amd.com> <98CBD80474FA8B44BF855DF32C47DC35E9F3F7@smartserver.smartshare.dk> <20240426081334.1a24577d@hermes.local> <98CBD80474FA8B44BF855DF32C47DC35E9F3FA@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: patches for DPDK stable branches <stable.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/stable>, <mailto:stable-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/stable/> List-Post: <mailto:stable@dpdk.org> List-Help: <mailto:stable-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/stable>, <mailto:stable-request@dpdk.org?subject=subscribe> Errors-To: stable-bounces@dpdk.org On Fri, 26 Apr 2024 17:17:25 +0200 Morten Br=C3=B8rup <mb@smartsharesystems.com> wrote: > > From: Stephen Hemminger [mailto:stephen@networkplumber.org] > > Sent: Friday, 26 April 2024 17.14 > >=20 > > On Fri, 26 Apr 2024 14:20:01 +0200 > > Morten Br=C3=B8rup <mb@smartsharesystems.com> wrote: > > =20 > > > > From: Ferruh Yigit [mailto:ferruh.yigit@amd.com] > > > > Sent: Thursday, 25 April 2024 18.53 > > > > > > > > Making 'rte_eth_stats_reset()' and 'rte_eth_xstats_reset()' APIs th= read > > > > safe has performance impact on datapath. > > > > > > > > Instead document APIs as not thread safe and add condition for reli= able > > > > stats reset functionality, forwarding should be stopped. =20 > > > > > > I'm not sure stopping forwarding suffices. > > > NIC hardware counters will keep progressing unless RX and TX is stopp= ed at =20 > > NIC level. =20 > > > > > > I don't have any suggestions for a better wording, though. :-( > > > > > > Anyway, better with the patch than without... > > > Acked-by: Morten Br=C3=B8rup <mb@smartsharesystems.com> > > > =20 > >=20 > > The safest option would be: > > rte_eth_dev_stop > > rte_eth_stats_reset > > rte_eth_dev_start =20 >=20 > Yes, but this will cause packet loss. > Network admins should be able to clear the counters without causing packe= t loss. >=20 Another alternative would be to a "reset zero" approach. When reset is done, capture the current state of all the relevant counters. Record that, and subtract those on next request. Never modify the underlying counters. To make it MT safe, use lock on reset and something super lightweight like seqlock on the stats request side. Might be hard with the size and va= riable length nature of xstats thoug.