From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Blechmann Subject: Re: scheduling latency & CONFIG_HZ Date: Sat, 14 Nov 2009 11:48:09 +0100 Message-ID: <4AFE8AE9.3050804@klingt.org> References: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigA3BD4369AAE78B59D206890C" Cc: linux-rt-users@vger.kernel.org To: Thomas Gleixner Return-path: Received: from mail.klingt.org ([86.59.21.178]:33640 "EHLO klingt.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753380AbZKNKsO (ORCPT ); Sat, 14 Nov 2009 05:48:14 -0500 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigA3BD4369AAE78B59D206890C Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable >> i am curious, do the values of CONFIG_HZ and CONFIG_NO_HZ somehow affe= ct the >> scheduling latency (as reported by cyclictest) of a real-time/vanilla = kernel, >> especially when CONFIG_HIGH_RES_TIMERS is enabled? >=20 > CONFIG_HZ should be pretty irrelevant, but CONFIG_NO_HZ=3Dy especially > when the CPU does support deeper C-States and the ACPI cpuidle support > is active may influence it simply because the wake up from deeper > c-states can take significantly longer than waking up from C1 (the > default halt state). Note that the wakeup latency from C-States > depends on the CPU model, chipset, available timer hardware ... interesting ... from my understanding, the wakeup latency is known to the kernel (/sys/devices/system/cpu/cpuX/cpuidle/stateY/latency) and is taken into account when governor selects the next state ... is it possible to tweak the governor by setting the latency requirement (pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY)) from userspace? thanks, tim --=20 tim@klingt.org http://tim.klingt.org Lesser artists borrow, great artists steal. Igor Stravinsky --------------enigA3BD4369AAE78B59D206890C Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkr+iukACgkQdL+4qsZfVsvDEQCdFS26AMyLYYaDUDro6tKocMK1 eiAAn1FI6eef0c5Yw/8mNw6Ec/jWShsL =XuKL -----END PGP SIGNATURE----- --------------enigA3BD4369AAE78B59D206890C--