From mboxrd@z Thu Jan 1 00:00:00 1970 From: Felipe Balbi Subject: Re: [RFC/NOT FOR MERGING] HACK: add global/private timers for A9 Date: Wed, 3 Jun 2015 16:54:45 -0500 Message-ID: <20150603215445.GK6042@saruman.tx.rr.com> References: <1433363565-17725-1-git-send-email-balbi@ti.com> <2466648.WjMxjIpAUG@wuerfel> <20150603210455.GD6042@saruman.tx.rr.com> <20150603212821.GH6042@saruman.tx.rr.com> <556F7493.2060602@codeaurora.org> Reply-To: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="vTUhhhdwRI43FzeR" Return-path: Received: from bear.ext.ti.com ([192.94.94.41]:50466 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753293AbbFCV5f (ORCPT ); Wed, 3 Jun 2015 17:57:35 -0400 Content-Disposition: inline In-Reply-To: <556F7493.2060602@codeaurora.org> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Stephen Boyd Cc: balbi@ti.com, Shawn Guo , Russell King , Arnd Bergmann , Tony Lindgren , Linux OMAP Mailing List , linux-arm-kernel@lists.infradead.org, slash.tmp@free.fr --vTUhhhdwRI43FzeR Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Wed, Jun 03, 2015 at 02:41:39PM -0700, Stephen Boyd wrote: > >>>>AM43xx, even though it's a single processor A9, it still has TWD and = global > >>>>timer. I was doing some profiling with RT v4.0 and latency is 3.5x lo= wer just > >>>>by switching from gptimer to twd/global. > >>>> > >>>>The only problem is that currently, is_smp() check prevents me from u= sing twd > >>>>with AM43xx (that's why it's commented below, for testing purposes). > >>>> > >>>>In the hopes that we can start a, hopefully, small thread around the = subject, > >>>>I'm sending this HACK which I used to get TWD and global timer enable= d so I > >>>>could measure latencies with cyclictest. > >>>> > >>>>Is it so that TWD shouldn't be available on UP integrations of ARM's = Cortex-A > >>>>processors ? > >>>> > >>>> > >>>I wondered about this recently when looking at something unrelated > >>>and noticed that the check had been introduced as part of > >>>904464b91eca8 ("ARM: 7655/1: smp_twd: make twd_local_timer_of_register= () > >>>no-op for nosmp"). > >>> > >>>I suspect this was just the wrong fix at the time, and that the > >>>real culprit is either alloc_percpu() or request_percpu_irq() > >>>getting called too early on a machine without SMP support. > >>> > >>>Possibly the problem is already resolved independently, if you > >>>didn't run into it. > >>no, no splats, nothing at all. See [1] > >> > >>[1] http://hastebin.com/helekubutu > >Adding Shawn > > >=20 > Mason was also interested in doing this. See [2]. From what I could tell > back then, commit 904464b91eca8 was working around the local timer APIs t= hat > no longer exist. >=20 > [2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/389931/focus=3D3= 92348 A lot of good information on that thread, thanks. Seems like getting twd/global timer working would also have some effect on context switching, perhaps ? cheers --=20 balbi --vTUhhhdwRI43FzeR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVb3elAAoJEIaOsuA1yqREN/UP/3v4pSbFRwd5D/SsZFOZcm02 TGfu93fpJQikvUBDtb6HEZSfJ+/RW/AhWPzkEZulg2Or54um6jQUEzsvQCyLxmOE CmW8chov9nYlgLax+NxKLomqbn+hfwvau9LC6PtLFpn5JLtbeGiWy4y312GnCpjN vIE6NYNvNgTgsEyF8H9VT2Jj4hwoljcG+OEZV5pAwI8G1yi7Lu0qs8qACH3Uph1+ wfWBQbd3buSDCcF4X/aDBFIamkAJxNE/eRdfuxmeVnrLu4Iiq8NzyKLwfogx4o8X 4r/9aLuHQxV9GufcAva9JFVlWedfCjtA4wVARkmP4FwX3N6IguveFgVFZVXMyH+3 MJfbVoaFD8tocbA6AOd3XgTo44jQFFV+9zryMxfgmfwT/v5aRnNoyJb7vypzJAUT 2T8Z0QJ/d/et2Zn/KN0wPHAUH+Vp5aF3R6sF7UQ7GQx0eEecL+HfSwCew1lHpHRu h2UXYA+ulQYdtgy8V67C6hUH8uC+ER0qswoY8tXXbS67XdHiYyf6EhygLyE+vjZ3 rjuy1dfI0n8oHoclOS2x0drO7vm3R0O+LkG5hxk93ky1+8T5izGfEVCs68pgu90i u17LvlUXv5s8RzzoPqhDlKAFmqG246SvNu3InF37Yh21JiSaPkisvIZetRHjZg88 8ETV71MGRF5MBhuLPEcT =Gs+P -----END PGP SIGNATURE----- --vTUhhhdwRI43FzeR--