From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C8A9243D515; Wed, 22 Jul 2026 21:40:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784756445; cv=none; b=e3R3XgCkQRcTF9JppCN+8oUNDppUMCx3k1cFR7E+HhpnPLWaFBVd9lzPobzcCE6qKzFZZe9ckmKHVhFu/o1HlXzFxFv8p8WZx4ETGF8PEHsIPa8fvd7JbKpq9O3EIj9wzXTLqGDLSBxvYS2gipHBaTnoePxvED/24fFAJNE/1Ss= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784756445; c=relaxed/simple; bh=xwr8LUCnrdENnKchnDT7SVKwsu61EN5Dq44EaIgFyFA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=NQ8pOgHArdkEJA9pa6vXfGIN6skmHDJZBDNiQEuCg5yhsN3cD/SZI6w4m8+Zssea8ibAUjecobpQKoK3/PAyla6uiTtj2/Wrxkcorr4damhnc6nkWbotU0DDDt2HewAZSURz95gOuAzNFQ3jvKMR4mTFCb1Ajt17o21LCK5B9XQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OEJuj4js; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OEJuj4js" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B5D11F000E9; Wed, 22 Jul 2026 21:40:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784756444; bh=WyMySADOfkdNBmTgBv+BFxJNFcV8ar22rjFpLcVIsQY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=OEJuj4js+JtTJv0NsZkWb23cfLqGJ4yOfUWB6+wNiXLXql714QOzMzTSTAVbaFiUp idzif4ciWotZpzFvCh7+k05v5RaQ7F2MQq6OUN7g45CC0qa5T/27dYV+NcUSLuPkHu x2NHvFm6NHrqrOe4B0BpZYEBDMr0JWkH3pU+kOeKU+uCjTN0omjH12vBTKeyXrCXuh RjIF9SpTcWbx3/FUyWFOj+XfXT01MlkO/az5dTx9lMpnkhnDIuDv9c0pKGS/p4jmpz 5U4Ao3XjEGNWMfZ7P67MjsUNWSCRgOWWuLaREbcyD+1BqfUmgGQIRJrMeoDOUMUV1v N+6igEw9pgRMQ== From: Will Deacon To: catalin.marinas@arm.com, rafael@kernel.org, lenb@kernel.org, saket.dumbre@intel.com, beata.michalska@arm.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, jeremy.linton@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, Pengjie Zhang Cc: kernel-team@android.com, Will Deacon , prime.zeng@hisilicon.com, wanghuiqiang@huawei.com, xuwei5@huawei.com, lihuisong@huawei.com, yubowen8@huawei.com, wangzhi12@huawei.com Subject: Re: [PATCH v2 0/2] CPPC: reduce FFH feedback-counter sampling skew on arm64 Date: Wed, 22 Jul 2026 22:39:35 +0100 Message-ID: <178475048433.1329854.7282103675861242164.b4-ty@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260708082818.808041-1-zhangpengjie2@huawei.com> References: <20260708082818.808041-1-zhangpengjie2@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit On Wed, 08 Jul 2026 16:28:16 +0800, Pengjie Zhang wrote: > The legacy CPPC feedback-counter path reads the delivered and reference > performance counters separately. > > On arm64 systems using AMU-backed CPPC FFH counters, each FFH read is > served through a cross-CPU counter read helper. Reading the counters > separately therefore widens the sampling window between them and can > skew the delivered/reference ratio used by cpuinfo_cur_freq. Under heavy > load, the skew is observable as transient values that may exceed the > platform maximum, as discussed in [1] and [2]. > > [...] Applied to arm64 (for-next/acpi), thanks! [1/2] ACPI: CPPC: add paired FFH feedback-counter read hook https://git.kernel.org/arm64/c/9aa7df520523 [2/2] arm64: topology: read CPPC FFH feedback counters in one operation https://git.kernel.org/arm64/c/42971d5329d9 Cheers, -- Will https://fixes.arm64.dev https://next.arm64.dev https://will.arm64.dev