Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755850Ab3DWNiy (ORCPT ); Tue, 23 Apr 2013 09:38:54 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:48783 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756448Ab3DWNix (ORCPT ); Tue, 23 Apr 2013 09:38:53 -0400 Message-ID: <51768EE3.6080005@pengutronix.de> Date: Tue, 23 Apr 2013 15:38:43 +0200 From: Marc Kleine-Budde User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: Greg Kroah-Hartman CC: Steffen Trumtrar , linux-kernel@vger.kernel.org, Jiri Slaby , "kernel@pengutronix.de" Subject: Re: [BUG] increased us/sys-load due to tty-layer in 2.6.38+ ?! References: <20130408092558.GD25003@pengutronix.de> <20130408150611.GB13824@kroah.com> <517595B7.1030000@pengutronix.de> In-Reply-To: <517595B7.1030000@pengutronix.de> X-Enigmail-Version: 1.5.1 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="----enig2APJUFGEGSLVVAERHVGBP" X-SA-Exim-Connect-IP: 2001:6f8:1178:4:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2607 Lines: 72 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2APJUFGEGSLVVAERHVGBP Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable On 04/22/2013 09:55 PM, Marc Kleine-Budde wrote: [...] >>> This resulted in >>> f23eb2b2b28547fc70df82dd5049eb39bec5ba12 >>> tty: stop using "delayed_work" in the tty layer >>> >>> as possible cause. Reverting this commit by hand in v3.8 showed a loa= d distribution >>> similar to 2.6.38. >>> What I haven't done, is measure if the load is really increasing or i= f top only >>> tells me so. Maybe the algorithm to calculate this somehow produces d= ifferent >>> results because of the switch from schedule_delayed_work to schedule_= work? >>> So, is this a bug, a feature, a symptom,...? >> >> It's a "fake" load (i.e. no extra cpu is being used, just a "busy" wai= t >> is happening.) The below test shows that with that offending patch, there is less time to calculate PI. My conclusion from this is that he patch increases the load generated by the processing of the serial line in the tty layer and/or increased overhead by more context switches/scheduling. > Another test was to measure how long it takes to calculate 10 k digits > of PI. Less time means less load on the system by the tty layer: >=20 > idle tty open serial load >=20 > v2.6.38-good 20.9s 22.3s 32.8s > v2.6.38-bad 20.9s 22.3s 51.5s Are there any options to decrease the load to the old value and keep the better latency introduce by that patch? Marc --=20 Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de | ------enig2APJUFGEGSLVVAERHVGBP Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlF2juYACgkQjTAFq1RaXHMaZgCgg8pvFSpK7FtXJ67SfKC6QXTu 0xkAniX86zIlYHxebMwPQ6Xcv7hrDaWt =KYcJ -----END PGP SIGNATURE----- ------enig2APJUFGEGSLVVAERHVGBP-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/