From nobody Mon May 25 15:33:28 2026 X-Original-To: freebsd-current@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4gPKfT0V9sz6fPYC for ; Mon, 25 May 2026 15:33:37 +0000 (UTC) (envelope-from olce@freebsd.org) Received: from smtp.freebsd.org (smtp.freebsd.org [IPv6:2610:1c1:1:606c::24b:4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "R12" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 4gPKfS5NFxz3qsx; Mon, 25 May 2026 15:33:36 +0000 (UTC) (envelope-from olce@freebsd.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1779723216; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GFQIpK6YK39u5fhdtAezzik+LWognzibWUbJDXgoIBY=; b=SyKsOXUnjFRtto9qJkDfotYeVX1X9Lrd9jpmh/9xw4B1i8BZeIvlKumDi4IpqpoCvsz0KZ FkEYu9osRXstsuHo1sWyVhnwAmH38mH67zuQJP//Fl38BpyDRCEyTBKm0kQy8eXCYtgiTt 9OWCBX7faKACKuuWluJ5BsUoxBIKAVOq25ymU8690vnPI86e5XCrTwTXbAj0TsaayxLLWm tQoaL2FftGIsPQ6Fq+6uj2ccDsbo7/mFpDW9otnU9heKsuPobmF5NXF+FHUUgiMd3WQ/ca E16hysaxQ+TqewKP2V5KmJepxyk3MwSNdsTKzNsghUlinZCGwoTKujLz8laekw== ARC-Seal: i=1; s=dkim; d=freebsd.org; t=1779723216; a=rsa-sha256; cv=none; b=xQJFLi84oW7M6sJEWRLU6NMIDRAVj8CUd3s0QxxRA3oBudJNzDLn7cSNJTvGyjO04TLKrp YPquLbduybDSwyB/CRgKgcw26mVZ4O1KEIFLtn2WyoFjrrPawW2JRuR7GBRtDFgCUdfn3e s0XgJ3PlTGyDbQjbg6jL2FpQGjnYChrrzrOvSPd1C2W0vxCKtu1p6sFZk/qsiE6wqzjbc8 iUXeRr3Sm5k2KisveCqo2HzLv5Q7bX8U7ZOB17ihORUwh+/RDDg3NR4f9TCVjsB5eJf1Qc 3oBI0pVmUBmAgAAEEMtpdZCXS600XSte35zDUdrRDZ/XQnk/nIdjEF99B/ErzQ== ARC-Authentication-Results: i=1; mx1.freebsd.org; none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1779723216; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GFQIpK6YK39u5fhdtAezzik+LWognzibWUbJDXgoIBY=; b=Q6z5gZwyODHGlIP4vlRCNznBkGuunFa9vCBsh2tAp+M5raghCp1igQVebSRCRdE3swWGhJ BuAm52wSFE/QWBlJ8e84tftwbBG0xRiBalSSyt1FkDFYB9JfUoCSznw+sIEuCX0Le14EXQ cMLzHz3lqKUnHfugXE8pbkkCO+Xsfpa4L4XbsCgw8JeI5hjNnAPy2WxZMH+JQMId12tVqi DShm/p0bk1e6N5z2byzfrL48UULVNR++zAonH8pg6dB5ZUsAxuLvv0WxQIKpOlgPBtnPV7 laMaDocT8c+jrlgquCUmaIVBhwoULA0vycbie/l/shAQMAp7LlWeLByDYKH6xg== Received: from ravel.localnet (lfbn-nic-1-328-19.w90-116.abo.wanadoo.fr [90.116.162.19]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) (Authenticated sender: olce/mail) by smtp.freebsd.org (Postfix) with ESMTPSA id 4gPKfS06HSzqJL; Mon, 25 May 2026 15:33:35 +0000 (UTC) (envelope-from olce@freebsd.org) From: Olivier Certner To: Warner Losh Cc: Chris Torek , Adrian Chadd , freebsd-current , ShengYi Hung Subject: Re: AMD, CPPC, etc Date: Mon, 25 May 2026 17:33:28 +0200 Message-ID: <29674359.QdLYigECfs@ravel> In-Reply-To: References: <1978836.vR5SVPPSqJ@ravel> List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@FreeBSD.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart3301997.VPuetLRq1i"; micalg="pgp-sha384"; protocol="application/pgp-signature" --nextPart3301997.VPuetLRq1i Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8"; protected-headers="v1" From: Olivier Certner To: Warner Losh Subject: Re: AMD, CPPC, etc Date: Mon, 25 May 2026 17:33:28 +0200 Message-ID: <29674359.QdLYigECfs@ravel> MIME-Version: 1.0 > At work, we run powerd on all our video streaming servers to save power by > ramping the cpu frequency up in times of high demand, and then back down > for low demand times.... it saves a lot of power. Yes, I'm aware (see our discussion with Andrew). Unless I'm mistaken, you're not using vanilla powerd(8) though. It's a very interesting use case, and something we would like to do in base FreeBSD coupled with CPPC. > But to interpret our performance data, we have to record the settings since 90% cpu at 800MHz is > way different than 90% at 3GHz... whatever we do here has to be observeable. This is where problems may come with CPPC, despite its parameters being observable. I remember reading somewhere (ACPI spec probably; don't have time to check right now) that the performance levels are to be *roughly* linear (they may have meant affine instead). As long as AMD continues to use only frequency levels to implement some CPPC performance level, affine regression could be perfect (but even that should be tested). If/when that changes, you will find yourself having to calibrate some model of CPPC levels to be able to compare 90% CPU at perf' level 127 and let's say 85% CPU at perf' level 128, and may never be able to do so with sufficient precision (depending on the exact hardware mechanisms used to implement the levels). Regards. -- Olivier Certner --nextPart3301997.VPuetLRq1i Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part. 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