From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clark Williams Subject: Re: cyclictest better values with system load than without (OMAP3530 target) Date: Tue, 26 Nov 2013 10:12:32 -0600 Message-ID: <20131126101232.21636c8f@sluggy> References: <5294681E.10406@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/Fqba.s6oc8HptI9v/TSTFE_"; protocol="application/pgp-signature" Cc: linux-rt-users@vger.kernel.org To: Stefan Roese Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6872 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757195Ab3KZQMe (ORCPT ); Tue, 26 Nov 2013 11:12:34 -0500 In-Reply-To: <5294681E.10406@gmail.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: --Sig_/Fqba.s6oc8HptI9v/TSTFE_ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable In my experience (on x86_64 mainly), that behavior (worse times when not under load) is due to the overhead of coming out of power-save/idle states. When you've got a big load on the system and all the cores are active, then the power-save logic and/or the idle logic doesn't kick in and devices aren't being powered down. Do you know if your OMAP has power-save logic available? Alternatively do you know how expensive the idle mechanism is? Have you tried booting with idle=3Dpoll then measuring without a load? Clark On Tue, 26 Nov 2013 10:21:34 +0100 Stefan Roese wrote: > Hi! >=20 > I'm running cylictest on a OMAP3530 target board and am a bit > astonished about the results. Especially that the latency values > are better on a system with system load (hackbench) than on one > without system load. Here the values I get: >=20 > With system load (hackbench): > ----------------------------- > # ./cyclictest -l 10000 -i 1000 -n -p 80 -q > # /dev/cpu_dma_latency set to 0us > T: 0 ( 1853) P:80 I:1000 C: 10000 Min: 36 Act: 156 Avg: 154 Max: > 244 >=20 > Idle system: > ------------ > # ./cyclictest -l 10000 -i 1000 -n -p 80 -q > # /dev/cpu_dma_latency set to 0us > T: 0 ( 2332) P:80 I:1000 C: 10000 Min: 81 Act: 530 Avg: 484 Max: > 602 >=20 >=20 > Some details to my test/system setup: > - Linux v3.8.13 > - preempt-rt patch 3.8.13-rt14 > - HW: TI OMAP3530 CM_T35 board > - Latest cyclictest from rt-tests git repository >=20 >=20 > I might have misconfigured the system. So here some extracts from > my .config: >=20 > ... > CONFIG_TICK_ONESHOT=3Dy > CONFIG_NO_HZ=3Dy > CONFIG_HIGH_RES_TIMERS=3Dy > ... > # CONFIG_CPU_FREQ is not set > # CONFIG_CPU_IDLE is not set > # CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED is not set > ... > CONFIG_PREEMPT_RT_FULL=3Dy > ... >=20 > With CONFIG_NO_HZ disabled I get slightly better results: >=20 > With system load (hackbench): > ----------------------------- > # ./cyclictest -l 10000 -i 1000 -n -p 80 -q > # /dev/cpu_dma_latency set to 0us > T: 0 ( 1840) P:80 I:1000 C: 10000 Min: 30 Act: 153 Avg: 154 Max: > 238 >=20 > Idle system: > ------------- > # ./cyclictest -l 10000 -i 1000 -n -p 80 -q > # /dev/cpu_dma_latency set to 0us > T: 0 ( 1371) P:80 I:1000 C: 10000 Min: 40 Act: 465 Avg: 435 Max: > 502 >=20 >=20 > Any ideas/explanations are really appreciated. >=20 > Thanks, > Stefan > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html --Sig_/Fqba.s6oc8HptI9v/TSTFE_ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlKUyHAACgkQHyuj/+TTEp3/uwCfR9vKVdDcQJniZg60lm+YiqNZ 8awAoOYCp9GQJiouTGdEYrOUDvCVAFRT =AuCm -----END PGP SIGNATURE----- --Sig_/Fqba.s6oc8HptI9v/TSTFE_--