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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r0Klj-001OIj-26; Tue, 07 Nov 2023 12:01:19 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1r0Klf-001OGe-2P; Tue, 07 Nov 2023 12:01:18 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by ams.source.kernel.org (Postfix) with ESMTP id 0DD9BB815F2; Tue, 7 Nov 2023 12:01:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E6A0C433C7; Tue, 7 Nov 2023 12:01:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699358473; bh=tVWRGGc71sN6ZG4ZOL5Bnx/rxUu20LoXAci7bQ26qpg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dBqe9XvBR+ZlWTzfjrZfXvXyM+zZdPEKwwYg2CIlyTrOS/DKjxejuSgEEgf2H37TG edaV5smRAEYnefcZu2Zh3/co1ONyekPN6FOgy4RVpmXzB9sg8+X2tc/jCd2ZPr/jAE 5lbbkGIf+rZk4850UpmwarrbeFDoY0KoZuw2awLB7p/y76Vtz0nDPQRC87LGtQmZIb Kj/EFJdN01iL4vLvgSu7N/XPyxOt97yKXs7t/YTkzGGE5zOzc5S41woEsklqRwZWDG qhmZiD22GJicMnFQ+HtBXkmq8ad33U0E7TrpVDebamqOp/DN6qrPez5725c61DBlFx z7FTxjR8WbDsQ== Date: Tue, 7 Nov 2023 12:01:03 +0000 From: Will Deacon To: Vincent Guittot Cc: linux@armlinux.org.uk, catalin.marinas@arm.com, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, sudeep.holla@arm.com, gregkh@linuxfoundation.org, rafael@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, viresh.kumar@linaro.org, lenb@kernel.org, robert.moore@intel.com, lukasz.luba@arm.com, ionela.voinescu@arm.com, pierre.gondois@arm.com, beata.michalska@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org, conor.dooley@microchip.com, suagrfillet@gmail.com, ajones@ventanamicro.com, lftan@kernel.org Subject: Re: [PATCH v5 7/7] arm64/amu: Use capacity_ref_freq to set AMU ratio Message-ID: <20231107120103.GA19367@willie-the-truck> References: <20231104105907.1365392-1-vincent.guittot@linaro.org> <20231104105907.1365392-8-vincent.guittot@linaro.org> <20231107103808.GF18944@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231107_040116_052301_B03FBEA3 X-CRM114-Status: GOOD ( 33.19 ) 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: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 07, 2023 at 12:18:20PM +0100, Vincent Guittot wrote: > On Tue, 7 Nov 2023 at 11:38, Will Deacon wrote: > > > > On Sat, Nov 04, 2023 at 11:59:07AM +0100, Vincent Guittot wrote: > > > Use the new capacity_ref_freq to set the ratio that is used by AMU for > > > computing the arch_scale_freq_capacity(). > > > This helps to keep everything aligned using the same reference for > > > computing CPUs capacity. > > > > > > The default value of the ratio (stored in per_cpu(arch_max_freq_scale= )) > > > ensures that arch_scale_freq_capacity() returns max capacity until it= is > > > set to its correct value with the cpu capacity and capacity_ref_freq. > > > > > > Signed-off-by: Vincent Guittot > > > --- > > > arch/arm64/kernel/topology.c | 26 ++++++++++++++------------ > > > drivers/base/arch_topology.c | 12 +++++++++++- > > > include/linux/arch_topology.h | 1 + > > > 3 files changed, 26 insertions(+), 13 deletions(-) > > > > > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topolog= y.c > > > index 817d788cd866..615c1a20129f 100644 > > > --- a/arch/arm64/kernel/topology.c > > > +++ b/arch/arm64/kernel/topology.c > > > @@ -82,7 +82,12 @@ int __init parse_acpi_topology(void) > > > #undef pr_fmt > > > #define pr_fmt(fmt) "AMU: " fmt > > > > > > -static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale= ); > > > +/* > > > + * Ensure that amu_scale_freq_tick() will return SCHED_CAPACITY_SCAL= E until > > > + * the CPU capacity and its associated frequency have been correctly > > > + * initialized. > > > + */ > > > +static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale= ) =3D 1UL << (2 * SCHED_CAPACITY_SHIFT); > > > > This doesn't seem to match the comment? SCHED_CAPACITY_SCALE doesn't ha= ve > > the '2 *' multiplier. > = > The comment in freq_inv_set_max_ratio() says: > = > * We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE=B2 > * in order to ensure a good resolution for arch_max_freq_scale for > * very low reference frequencies (down to the KHz range which should > * be unlikely). > = > Then there is a " * arch_max_freq_scale) >> SCHED_CAPACITY_SHIFT" > when computing the scale which brings the result back to > SCHED_CAPACITY_SHIFT Ah, I see; I'd not spotted that amu_scale_freq_tick() is doing some arithmetic on the value (it doesn't return anything because it's 'void'). It's slightly confusing because the comment talks about SCHED_CAPACITY_SCALE whereas all the code works on the shift, but I get it now. > > > static DEFINE_PER_CPU(u64, arch_const_cycles_prev); > > > static DEFINE_PER_CPU(u64, arch_core_cycles_prev); > > > static cpumask_var_t amu_fie_cpus; > > > @@ -112,14 +117,14 @@ static inline bool freq_counters_valid(int cpu) > > > return true; > > > } > > > > > > -static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rat= e) > > > +void freq_inv_set_max_ratio(int cpu, u64 max_rate) > > > { > > > - u64 ratio; > > > + u64 ratio, ref_rate =3D arch_timer_get_rate(); > > > > > > if (unlikely(!max_rate || !ref_rate)) { > > > - pr_debug("CPU%d: invalid maximum or reference frequency= .\n", > > > + WARN_ONCE(1, "CPU%d: invalid maximum or reference frequ= ency.\n", > > > cpu); > > > - return -EINVAL; > > > + return; > > > } > > > > > > /* > > > @@ -139,12 +144,12 @@ static int freq_inv_set_max_ratio(int cpu, u64 = max_rate, u64 ref_rate) > > > ratio =3D div64_u64(ratio, max_rate); > > > if (!ratio) { > > > WARN_ONCE(1, "Reference frequency too low.\n"); > > > - return -EINVAL; > > > + return; > > > } > > > > > > - per_cpu(arch_max_freq_scale, cpu) =3D (unsigned long)ratio; > > > + WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ra= tio); > > > > Why is WRITE_ONCE() now needed? > = > the tick can already use it. We want to make sure to use either the > old or the new one but not an intermediate value Isn't that already the case without this patch? In other words, this should be a separate change. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel