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Wed, 13 Aug 2025 12:30:17 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: Tf2626a88c2a27380 Date: Wed, 13 Aug 2025 18:29:37 +0200 From: "Arnd Bergmann" To: "Catalin Marinas" , "Ankur Arora" Cc: linux-kernel@vger.kernel.org, Linux-Arch , linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org, "Will Deacon" , "Peter Zijlstra" , "Andrew Morton" , "Mark Rutland" , harisokn@amazon.com, cl@gentwo.org, "Alexei Starovoitov" , "Kumar Kartikeya Dwivedi" , zhenglifeng1@huawei.com, xueshuai@linux.alibaba.com, "Joao Martins" , "Boris Ostrovsky" , "Konrad Rzeszutek Wilk" , "Rafael J . Wysocki" , "Daniel Lezcano" Message-Id: <67b6b738-0f1c-4dd4-817d-95f55ec9272b@app.fastmail.com> In-Reply-To: References: <20250627044805.945491-1-ankur.a.arora@oracle.com> <20250627044805.945491-2-ankur.a.arora@oracle.com> <877bz98sqb.fsf@oracle.com> Subject: Re: [PATCH v3 1/5] asm-generic: barrier: Add smp_cond_load_relaxed_timewait() Content-Type: text/plain Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250813_093022_506049_AD169996 X-CRM114-Status: GOOD ( 14.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Aug 13, 2025, at 18:09, Catalin Marinas wrote: > On Mon, Aug 11, 2025 at 02:15:56PM -0700, Ankur Arora wrote: > >> This also gives the WFET a clear end time (though it would still need >> to be converted to timer cycles) but the WFE path could stay simple >> by allowing an overshoot instead of falling back to polling. > > For arm64, both WFE and WFET would be woken up by the event stream > (which is enabled on all production systems). The only reason to use > WFET is if you need smaller granularity than the event stream period > (100us). In this case, we should probably also add a fallback from WFE > to a busy loop. I think there is a reasonable chance that in the future we may want to turn the event stream off on systems that support WFET, since that is better for both low-power systems and virtual machines with CPU overcommit. Arnd