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Thu, 29 Jan 2026 12:27:33 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface 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 MIME-Version: 1.0 X-ThreadId: AQpxQpBrI0Yc Date: Thu, 29 Jan 2026 12:27:13 -0500 From: "Drew Gallatin" To: "Olivier Certner" , "Gleb Smirnoff" Cc: freebsd-current@freebsd.org, src-committers@freebsd.org, "ShengYi Hung" Message-Id: <6197e075-212f-4260-b437-902e06d1002b@app.fastmail.com> In-Reply-To: <2329920.sMrx5ctUpN@ravel> References: <2329920.sMrx5ctUpN@ravel> Subject: Re: January 2026 stabilization week Content-Type: multipart/alternative; boundary=7733fe59e5f4415e81a0e3d20dfd9617 --7733fe59e5f4415e81a0e3d20dfd9617 Content-Type: text/plain Content-Transfer-Encoding: 7bit On Thu, Jan 29, 2026, at 3:47 AM, Olivier Certner wrote: > > For now, it's either CPPC or powerd(8) (as for Intel), and a priori I'd recommend switching to CPPC entirely (once we have finished with the potential problems here). For pressing production issues, in the meantime you can set the 'machdep.hwpstate_amd_cppc_enable' tunable to 0 to force using the "manual" P-states that powerd(8) can manipulate. > On Intel, and now on AMD, it seems that CPPC is far worse than powerd (*). By that I mean that low power settings use the same amount of power as powerd when ramped down, but limit the performance when a server is busy. Conversely, midrange settings use more power than powerd and provide less performance. And high settings use more power. (*) At Netflix, we use a modified powerd, similar to powerdxx that takes multi-core load into account. So the ability to let software control frequency is something that I don't want to loose. Drew --7733fe59e5f4415e81a0e3d20dfd9617 Content-Type: text/html Content-Transfer-Encoding: quoted-printable


On Thu, Jan 29, 2026, at 3:47 AM, Olivier Certner wrot= e:

For now, it's either CPPC or powerd(8) (as for Intel), and a priori I= 'd recommend switching to CPPC entirely (once we have finished with the = potential problems here).  For pressing production issues, in the m= eantime you can set the 'machdep.hwp= state_amd_cppc_enable' tunable to 0 to force using the "manual" P-st= ates that powerd(8) can manipulate.


On Intel, and now on AMD, it seems that CPPC is far wor= se than powerd (*).  By that I mean that low power settings use the= same amount of power as powerd when ramped down, but limit the performa= nce when a server is busy.   Conversely, midrange settings use= more power than powerd and provide less performance.  And high set= tings use more power.

(*) At Netflix, we use a = modified powerd, similar to powerdxx that takes multi-core load into acc= ount.

So the ability to let software control fr= equency is something that I don't want to loose.

Drew --7733fe59e5f4415e81a0e3d20dfd9617--