From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx.itxnorge.no (itx-kvm-14.itxnorge.no [91.189.121.228]) (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 0DDBD3A3830 for ; Tue, 6 Oct 2026 11:38:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.189.121.228 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791286723; cv=none; b=Pqef3iG4jmpFEHLpqh3U99IwshHU4rlpPjbTL8m1MPLLJ0hUhn4g8pw5PuYkqv7SJt/WkcuuMSDMpgi1fY+/t69uuuCX1vu79uJ/EpcBvdYGS7Ah2L0obGxIGwTODIAjJUs/pSPqx4cXFT6RH+T4a88C3Yz6pWf1OIm8JoETBfU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791286723; c=relaxed/simple; bh=bpwXiLYMy1C9YaNTlOPiapR+LCEmQ1cY/6Va6pUCLvQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Y8gDXD5HFIgP6wELtYFii5VNxTTbkIsI/7w1zbfIIToU0apuQOi/rGO16S06Zl07EgL4CEMmfEySNV8VvyQyyVery7vvQCZ65XkVWUl6RTNc1E1UGQeCJyAJcpX4GJ5uCBXhwLO2E5N3lE50fuepJtxLxeIAKQ5USYHIoiUqCis= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=itx.no; spf=pass smtp.mailfrom=itx.no; dkim=pass (1024-bit key) header.d=itx.no header.i=@itx.no header.b=SXFfQnVu; arc=none smtp.client-ip=91.189.121.228 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=itx.no Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=itx.no Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=itx.no header.i=@itx.no header.b="SXFfQnVu" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=itx.no; s=mx.itx.no; t=1791286719; 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=bpwXiLYMy1C9YaNTlOPiapR+LCEmQ1cY/6Va6pUCLvQ=; b=SXFfQnVu3C5qw7ftRs2BkjBoFpdhElh7spjqmwjFPjcCGTzgs7zxIMh0EDaIIaBMAaiHge dzqHdmNdU4tVWAFu4iEHDy8mT0IrNGO91SyBkm1GLCGrq6S+PfVoqwdEfdHqgE3FcLbR03 PxGYS8Lghev0LvslLrsdQzcZXWF8fto= Subject: Re: [PATCH v2] sched/cputime: Don't account idle time twice after dyntick-idle From: Stian Halseth To: Frederic Weisbecker Cc: Thomas Gleixner , Anna-Maria Behnsen , Ingo Molnar , Peter Zijlstra , Shrikanth Hegde , regressions@lists.linux.dev, linux-kernel@vger.kernel.org Date: Tue, 06 Oct 2026 13:38:38 +0200 In-Reply-To: References: <20261005194010.168299-1-stian@itx.no> <630a98619b9c5d04b01dd1c506d432d13f724218.camel@itx.no> Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-JmipPCAzG8QhmldjCN+a" Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 --=-JmipPCAzG8QhmldjCN+a Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable On Tue, 2026-10-06 at 13:19 +0200, Stian Halseth wrote: > On Tue, 2026-10-06 at 13:08 +0200, Frederic Weisbecker wrote: >=20 > > > Only with steal time, and that is older than the rework. I ran > > > the > > > same > > > guest test on v7.1 and on ad5a9e14ec8b, the parent of > > > cf6444c3e1bb7. > > > Total CPU time per wall second on the loaded vCPU: > > >=20 > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0 v7.1=A0=A0=A0 ad5a9e14ec8b=A0=A0 v2 > > > =A0 3.7 ms sleeps=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0.995=A0=A0 0.996=A0= =A0=A0=A0=A0=A0=A0=A0=A0 0.998 > > > =A0 pipe ping-pong=A0=A0=A0=A0=A0=A0=A0=A0=A0 0.997=A0=A0 0.996=A0=A0= =A0=A0=A0=A0=A0=A0=A0 1.000 > > > =A0 steal, sleep + spin=A0=A0=A0=A0 1.029=A0=A0 1.028=A0=A0=A0=A0=A0= =A0=A0=A0=A0 1.008 > > > =A0 steal, pipe ping-pong=A0=A0 1.338=A0=A0 1.341=A0=A0=A0=A0=A0=A0= =A0=A0=A0 1.001 > > >=20 > > > Without steal time nothing was counted twice before the rework. > > > With > > > steal time, v7.1 counted steal time during idle as both idle and > > > steal > > > time. The rework fixed most of that, and what is left with a busy > > > spin > > > after each wakeup is smaller than before. > >=20 > > Ok and you haven't observed a real difference between your v1 and > > v2, > > right? > >=20 > No, not in normal operation.=20 >=20 > It only made a difference with a test-only change that stops the tick > on every idle entry. There v2 added to a pending overlap about 900 > times a second, which v1 lost. >=20 > /Stian >=20 IMO the pre-existing steal time issue is out of scope for this patch, and would require a separate investigation, _if_ it's worth the time. --=-JmipPCAzG8QhmldjCN+a Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTK1ph9OaYoND1R57zoeAEuJe36VgUCasTdvgAKCRDoeAEuJe36 VhJkAQCe7Acr1ntD8/N2KSJKX4HG2fhUj9XV93ul1fQh2R6PrgEAvNCbfzVcDYUJ M7aFZRR3byX3ovqJEL0Xc4R3wRZxOQM= =EBSv -----END PGP SIGNATURE----- --=-JmipPCAzG8QhmldjCN+a--