Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793969289; b=UrED4B0+Op9ABTp9g4aJRae9AvyLMHkifmmRtGzdlOJIoVJTSByMWP5Ql7r8A2cuhC7M xDgQNPor6iwnZFOWdrJb/Qhs+RPop6XBQUUWwgGFahAx2Xzq8iQ+98K5JUndpSljany1s jg0ljCiC8cpXTF5YueLiuztdxcPHETFmuxlMbbDemI4bns6RoVgiQGBgYIV9mSPuRqBDF kSAyZPq6sKaB0EeL0Thwdfr0idOYQRcJYtyqQFotMyvH+BJSHSdCBoiWOnMb2yr6R5Fm5 d+iWyTVZGpaNWYrQ5ko8VPgEfaHXVUlX/LLalA91Gz7NVY1BBeK92nW/rUr6mCf2/ng== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793969289; h=Received:DKIM-Signature:Message-ID:From:Subject:Reply-To:To:Cc: In-Reply-To:References:Content-Type:Content-Transfer-Encoding:Date; bh=MhwEQoJtNRZJlmrEs1A89vUyPLNxq1vGL/oAu4Qw9nQ=; b=w90bhs3I8LV2yjVP1yEG7fud0TzNTHYMYDUjTQ/YfI3D+TyKaWC7M2VnlIE4/VGYVX/J ZQEBF+GJl19uh6uiVHuFr/eL9Lz9iz6C8ues2Y+xpMhLLoPj2ih+8a0+gQ9l+SWKbbQ1u j4zsjbdXGA5rR0XgcrsDOBURyI5XIuGW9/bR04nfjp10nSB3u+jjgaIM3haYlphW0p4OS MLgFI0/5WqutS1QyJqZe1JPg0u5XpcWxh98i4K3h5I4l3Dh6OCiMuTtm8azRMLMcuFwap JI4yMJjpRRzXUoACqlaXSFYesUaTkz+mEIGwY34VqpsTLRHXoVyf7NRuMJQqHpB84qA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QEZC1ajG; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84FA9606A329 for ; Fri, 6 Nov 2026 12:48:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QEZC1ajG Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0E0B1F0089F; Fri, 6 Nov 2026 12:48:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793969289; bh=MhwEQoJtNRZJlmrEs1A89vUyPLNxq1vGL/oAu4Qw9nQ=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=QEZC1ajGvVl/McDsnQEB5p6zWU7QRsRfYMtkhohfy+zZZy2hKpyxACVOkrK/yl9pp R07GnYnToOfcYaDoGxWVNlVu0XmG52uPZYghGk4qglLzf+Lqa4ZOaHJVNkkas+XrvS 3KBeIZaesGeJYY40RbWDAtbu4QKxrzMDqKwZEPVuvdQayVC+cM0G335boFnOC1ml13 rXR91kpL8zW71pSmtMe0xz9oTSaOccMfoiegpEzdFtsZoE8YWcQxqa3G8BJP4oLPRQ 8aS0+GgSDFNmMYQeHa7lFMI3Kr6/W2MPdQbjnv6HrsTeBoCk7NSBx5Xq4rERSrr2fz dtC27kmxGEtcQ== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH] sched: Decouple PREFERRED_CPU from PARAVIRT Reply-To: sashiko-reviews@lists.linux.dev To: "Mete Durlu" Cc: linux-s390@vger.kernel.org, "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Christian Borntraeger" In-Reply-To: <20261106-preferredcpu-v1-1-3f0ca4944f8b@linux.ibm.com> References: <20261106-preferredcpu-v1-1-3f0ca4944f8b@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 06 Nov 2026 12:48:08 +0000 X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list > PREFERRED_CPU mechanism does not rely on any feature introduced by PARAVI= RT > but PREFERRED_CPU still gated behind PARAVIRT. Any architecture that > would like to enable PREFERRED_CPU mechanism has to also enable PARAVIRT > and bring additional changes to accommodate PARAVIRT's requirements. >=20 > As an example, s390 doesn't enable PARAVIRT config for hardware virtualiz= ed > Logical Partitions (LPAR). The steal time is accounted for the LPARs via > architecture's own steal time accounting mechanism instead of the common > steal time infrastructure PARAVIRT supplies. > For s390 to enable PREFERRED_CPU, PRAVIRT and its required stubs are > just unncessary. >=20 > Based on the discussion between Yury Norov and Peter Zijlstra over > Yury's original patch [1]: >=20 > Introduce a new config flag HAVE_CPUTIME_STEAL to indicate that the > architecture has steal time measurement capabilities already implemented > and to signal that PARAVIRT is not required. > Remove PARAVIRT gating from CPU_PREFERRED and add HAVE_CPUTIME_STEAL > instead. > Select HAVE_CPUTIME_STEAL for s390 and powerpc-pseries configs. >=20 > [1] https://lore.kernel.org/all/20261101192203.6979-2-ynorov@nvidia.com/ >=20 > Reviewed-by: Yury Norov > Suggested-by: Peter Zijlstra > Signed-off-by: Mete Durlu Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261106-preferredc= pu-v1-1-3f0ca4944f8b@linux.ibm.com?part=3D1