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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wiBOh-000000051Zo-0aVi; Fri, 10 Jul 2026 13:36:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wiBOe-000000051Yd-2XA3 for linux-arm-kernel@lists.infradead.org; Fri, 10 Jul 2026 13:36:06 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 39421176A; Fri, 10 Jul 2026 06:35:56 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B1F2B3F66F; Fri, 10 Jul 2026 06:35:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783690560; bh=O6yfiHmVjh++kj3mIFoELPTa5h6lT7CwpxKruuuvLMs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GOhfvWktQwk8Z6pT+9xg9fGgKpYRyGuz87RGFGcQRsoQU9yRQL/g8kW4uoBdmwIMj 9BcXC/cGWW13telbDkMt7/LPm4bToQIOMAo/WnFLixmG8wuOriEbn36MPX6ezToN8f Gj4d3NcjYxIlNJ9i6dP1Kwu/VH91CgYwwxQ52VKk= Date: Fri, 10 Jul 2026 15:35:48 +0200 From: Beata Michalska To: Jeremy Linton Cc: Pengjie Zhang , catalin.marinas@arm.com, will@kernel.org, rafael@kernel.org, lenb@kernel.org, saket.dumbre@intel.com, zhenglifeng1@huawei.com, sumitg@nvidia.com, zhanjie9@hisilicon.com, geert+renesas@glider.be, cuiyunhui@bytedance.com, vanshikonda@os.amperecomputing.com, ionela.voinescu@arm.com, viresh.kumar@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, acpica-devel@lists.linux.dev, linuxarm@huawei.com, prime.zeng@hisilicon.com, wanghuiqiang@huawei.com, xuwei5@huawei.com, lihuisong@huawei.com, yubowen8@huawei.com, wangzhi12@huawei.com Subject: Re: [PATCH v2 2/2] arm64: topology: read CPPC FFH feedback counters in one operation Message-ID: References: <20260708082818.808041-1-zhangpengjie2@huawei.com> <20260708082818.808041-3-zhangpengjie2@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260710_063604_718773_AC7C978E X-CRM114-Status: GOOD ( 26.64 ) 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 Thu, Jul 09, 2026 at 01:11:13AM -0500, Jeremy Linton wrote: > Hi, > > On 7/8/26 3:28 AM, Pengjie Zhang wrote: > > arm64 implements CPPC FFH feedback-counter reads using AMU counters. > > Because those counters must be sampled on the target CPU, reading the > > delivered and reference counters separately widens the observation window > > between them. > > > > Implement the paired FFH feedback-counter read hook on arm64 and sample > > both AMU counters together before decoding the requested CPC register > > values. > > > > Also factor the FFH bitfield extraction logic into a helper and reuse > > it from the existing single-counter FFH read path. > > > > Tested-by: Sumit Gupta > > Reviewed-by: Sumit Gupta > > Tested-by: Vanshidhar Konda > > Reviewed-by: Vanshidhar Konda > > Signed-off-by: Pengjie Zhang > > --- > > arch/arm64/kernel/topology.c | 92 ++++++++++++++++++++++++++++++++---- > > 1 file changed, 84 insertions(+), 8 deletions(-) > > > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > > index b32f13358fbb..d28438f8b83f 100644 > > --- a/arch/arm64/kernel/topology.c > > +++ b/arch/arm64/kernel/topology.c > > @@ -373,6 +373,16 @@ core_initcall(init_amu_fie); > > #ifdef CONFIG_ACPI_CPPC_LIB > > #include > > +struct amu_ffh_ctrs { > > + u64 corecnt; > > + u64 constcnt; > > +}; > > + > > +enum cpc_ffh_ctr_id { > > + CPC_FFH_CTR_CORE = 0x0, > > + CPC_FFH_CTR_CONST = 0x1, > > +}; > > + > > static void cpu_read_corecnt(void *val) > > { > > /* > > @@ -397,7 +407,7 @@ static void cpu_read_constcnt(void *val) > > } > > static inline > > -int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val) > > +int counters_read_on_cpu(int cpu, smp_call_func_t func, void *val) > > { > > /* > > * Abort call on counterless CPU. > > @@ -447,24 +457,90 @@ bool cpc_ffh_supported(void) > > return true; > > } > > +static void amu_read_core_const_ctrs(void *val) > > +{ > > + struct amu_ffh_ctrs *ctrs = val; > > + > > + /* > > + * cpu_read_constcnt() incurs slight latency due to the > > + * ARM64_WORKAROUND_2457168 check. Read it first to minimize > > + * the sampling skew between the const and core counters. > > + */ > > + cpu_read_constcnt(&ctrs->constcnt); > > + cpu_read_corecnt(&ctrs->corecnt); > > +} > > + > > +static u64 cpc_ffh_extract_bits(const struct cpc_reg *reg, u64 val) > > +{ > > + val &= GENMASK_ULL(reg->bit_offset + reg->bit_width - 1, > > + reg->bit_offset); > > + val >>= reg->bit_offset; > > + > > + return val; > > +} > > + > > +static void cpc_ffh_ctr_value(const struct cpc_reg *reg, > > + const struct amu_ffh_ctrs *ctrs, u64 *val) > > +{ > > + switch ((u64)reg->address) { > > + case CPC_FFH_CTR_CORE: > > + *val = ctrs->corecnt; > > + break; > > + case CPC_FFH_CTR_CONST: > > + *val = ctrs->constcnt; > > + break; > > + } > > + > > + *val = cpc_ffh_extract_bits(reg, *val); > > +} > > + > > +static bool is_amu_ctr_reg(const struct cpc_reg *reg) > > +{ > > + return reg->address == CPC_FFH_CTR_CORE || > > + reg->address == CPC_FFH_CTR_CONST; > > +} > > + > > +int cpc_read_ffh_fb_ctrs(int cpu, struct cpc_reg *reg1, u64 *val1, > > + struct cpc_reg *reg2, u64 *val2) > > +{ > > + struct amu_ffh_ctrs ctrs; > > + int ret; > > + > > + if (!is_amu_ctr_reg(reg1) || !is_amu_ctr_reg(reg2)) > > + return -EINVAL; > > + > > + ret = counters_read_on_cpu(cpu, amu_read_core_const_ctrs, &ctrs); > > + if (ret) { > > + /* > > + * If AMU is unsupported (-EOPNOTSUPP), translate the error > > + * to -ENODEV. This explicitly tells the generic CPPC layer > > + * to abort immediately and avoid falling back to pointless > > + * single-counter reads. > > + */ > > + return ret == -EOPNOTSUPP ? -ENODEV : ret; > > + } > > + > > + cpc_ffh_ctr_value(reg1, &ctrs, val1); > > + cpc_ffh_ctr_value(reg2, &ctrs, val2); > > + > > + return 0; > > +} > > + > > int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val) > > { > > int ret = -EOPNOTSUPP; > > switch ((u64)reg->address) { > > - case 0x0: > > + case CPC_FFH_CTR_CORE: > > ret = counters_read_on_cpu(cpu, cpu_read_corecnt, val); > > break; > > - case 0x1: > > + case CPC_FFH_CTR_CONST: > > ret = counters_read_on_cpu(cpu, cpu_read_constcnt, val); > > break; > > } > > - if (!ret) { > > - *val &= GENMASK_ULL(reg->bit_offset + reg->bit_width - 1, > > - reg->bit_offset); > > - *val >>= reg->bit_offset; > > - } > > + if (!ret) > > + *val = cpc_ffh_extract_bits(reg, *val); > > return ret; > > } > > > So, more a nitpik that only applies if this set gets respun, but: > > I don't think this FFH counter logic belongs in the arm64 topology.c file, > its not really topology related. I agree. Those bits should be moved. That said, I think it would be best to land this first, as it addresses a rather long-standing issue. We can do the cleanup later. If needed, I'd pick it up soon'ish. --- BR Beata > > > > >