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Thu, 4 Jul 2024 14:59:31 -0400 (EDT) From: Thomas Monjalon <thomas@monjalon.net> To: Stephen Hemminger <stephen@networkplumber.org> Cc: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>, Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>, Tyler Retzlaff <roretzla@linux.microsoft.com>, Ruifeng Wang <Ruifeng.Wang@arm.com>, "dev@dpdk.org" <dev@dpdk.org>, nd <nd@arm.com>, Dhruv Tripathi <Dhruv.Tripathi@arm.com>, Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>, Jack Bond-Preston <jack.bond-preston@foss.arm.com>, Nick Connolly <Nick.Connolly@arm.com>, Vinod Krishna <Vinod.Krishna@arm.com>, "david.marchand@redhat.com" <david.marchand@redhat.com> Subject: Re: [PATCH v2 2/2] eal: add Arm WFET in power management intrinsics Date: Thu, 04 Jul 2024 20:59:29 +0200 Message-ID: <3741901.S9oNm88NmQ@thomas> In-Reply-To: <20240704075515.75a9a0cd@hermes.local> References: <20240604044401.3577707-2-wathsala.vithanage@arm.com> <4208140.dumfJixkPq@thomas> <20240704075515.75a9a0cd@hermes.local> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions <dev.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/dev>, <mailto:dev-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/dev/> List-Post: <mailto:dev@dpdk.org> List-Help: <mailto:dev-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/dev>, <mailto:dev-request@dpdk.org?subject=subscribe> Errors-To: dev-bounces@dpdk.org 04/07/2024 16:55, Stephen Hemminger: > On Thu, 04 Jul 2024 16:14:42 +0200 > Thomas Monjalon <thomas@monjalon.net> wrote: >=20 > > > > Let=E2=80=99s ask Pavan why this flag is used in cn10k driver. > > > >=20 > > > > From our perspective, WFE is available on all the supported arm pla= tforms in > > > > DPDK. > > > > Therefore, RTE_ARM_USE_WFE should be treated as a flag to choose be= tween > > > > WFE > > > > and non-WFE code paths due to performance reasons rather than as a = flag > > > > that indicates > > > > the availability of the instruction on the target CPU. > > > > =20 > > >=20 > > > We are using this flag to allow application to choose between WFE and= non-WFE code path. > > > The non-WFE path performs slightly better. =20 > >=20 > > What's the benefit of the WFE path then? >=20 > WFE saves power at the expense of latency. Yes maybe there is a misunderstanding. Pavan can you confirm you were saying "throughput is better on non-WFE"? but "power consumption is lower on WFE path"? > Maybe some form of hybrid approach would work best and could > be always used. >=20 > For example, many implementations of mutex do a short spin poll > then fall back to a waiting primitive (like futex).