From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout.gmx.net (mout.gmx.net [212.227.17.22]) (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 6BCDF2773F0 for ; Tue, 21 Apr 2026 03:55:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=212.227.17.22 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776743725; cv=none; b=QBupuvdmNbkj008+tNu3qlTS/ICJnjkUkO9O6kLWX0IK+0+CkeEaA+5B3SCA3sBeQ1eOnN6qodbnsIhGpqbLRCGLGgNLVpSQLy5bX3G1CKW1XNUO6w051Xwf/8v6RJ2/zs51QCr+ziN6zIAYeJ5/wKe5eRl3XH7EZTHuN7lX70I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776743725; c=relaxed/simple; bh=jObQrtTCEoALGpdyLsTpen9YiPKh68yUZAmgNjftPdQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; 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linux-kernel@vger.kernel.org Date: Tue, 21 Apr 2026 05:55:15 +0200 In-Reply-To: References: <2877d886d8470f4ea3393e8c2e570a059c2b8b1b.camel@gmx.de> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Provags-ID: V03:K1:l4vj2rCWQDNSaxPBr2bIL9hloK7K97srCmOnpP7F4KLJRHDRWVf 1zmmXkr9Wp/voP37CKqoJSDOW8ekdLhkhx83C1PsdSTIJUXlVjNWx/PDnDQNOraaPrXZFRK YaqCNGyY0GODJCgx8rzEW26aoQW0glkozcxcuNVvSlDDbRD653lwAKxHoO+l0Pr4jGcMK2V Pe0oTecXHR9wwqI4t9cVQ== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:893zmmCTuHQ=;hDHyVdwMnJ/5eU02WYuGTdUJxF4 feEdga5c/vD+E1IOx172N5fu1efRRXcxB69C4Mx9eDzFOEtBfChNS+r45XeiCsBaH5TEJl6rn sb+csMNKjuEDfixPXm7XBrrS2ZNLX7KsUyG/Yi+PKNmyjEax/RPiQLUpUsQzG68s/Xvz168X0 +qgapr4eb8gBgdmmQCg++25LYtyXDF/v7GnyOZLkVMaSWQDjdXXCjDoehcKIL4Ysswrxl+xx4 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80r0ufNawVAMTXM1G2fM9aNJ14vgzQIhyhoP0Eqv0uvRqALhgpfpaCGKkyqC+99aOEzx+LQIX ehWsI9Hd8rZhZr9SXNueSDw1LnN1f3Ksec2NixhuQDR2SQzsOhYp/irlfH3bNN9N01lX4Hk8Q SL91VsPbPK4o06jTzdtmbZczMF3CrqoUDXstH8LrrM2o2SiB3RRDRyiXslDqu3qIlw6QdTuzh xv6BzFRVQlq4VaJTQgAtp3qSpbT7JrivGjG9/UkdD7lkgG+QzF21ZntBy9JaPUZayAY7MpWdB UP1xF+fJBaYD/38FHy2dUY5RHXVLVB453dxBqd4vMIrwFurESDJ0oBhADlmcWxRkm6GE+Z6cP 8UJjEqAYfvyMRyfbuiwZX/xuK0JVKYvFsCqaGOAA2cnJkMfMmtcrtXkXmyxNNgRSClgc7+83S wX+1OYvY4r8g8AdFg18bFswSaqxEkHMCCJ8f5dTT7Rd53wwRoiIkzspa08LBXTETvGmCsgC8Q RZ1drGmFUZUj/YVRQrHACrmo7zT+qEkIgH01zl0qB73BEPQD4kAsWOSFMuj3T51gC4V/tb8Nh 8ody9RXgUimgKYdPp6jMI9I07MYB37CsixNE= On Mon, 2026-04-20 at 12:59 +0200, Tom Gebhardt wrote: > Hi Mike, >=20 > thank you for testing =E2=80=94 but I notice that your data only shows 6.= 12.75 > with DELAY_DEQUEUE on/off. There is no 6.6 baseline in your results. > That is the comparison that matters: 6.6 vs 6.12 on the same hardware > with the same tool. >=20 > There is also a version difference worth noting: you are running > stress-ng 0.21.00, while our measurements used stress-ng 0.15.06 =E2=80= =94 > which was the version available on Raspberry Pi OS Bookworm at the > time of the original report. The pipe stressor calculation changed > significantly between those versions. >=20 > This creates an uncomfortable coincidence: a measurable scheduler > regression was introduced in 6.12 (DELAY_DEQUEUE), and around the same > time the standard measurement tool changed how it calculates the pipe > benchmark score. The result is that the regression becomes invisible > when comparing with the newer tool version =E2=80=94 not because it was f= ixed, > but because the metric changed. Aha. > Would you be willing to run the 6.6 comparison with stress-ng 0.15.06 > on your Pi 5? No need, your reported DELAY_DEQUEUE impact for 6.12.75+rpt-rpi-2712 appeared with stress-ng 0.15.06. However, my local 6.12.y branch kernel, which has all eevdf fixes as well as Peter's still pending sched/ttwu series, still does NOT repro. git@homer:..git/raspberrypi-kernel> quilt applied|grep delay patches/eevdf/WIP/0043-sched-fair-Removed-unsued-cfs_rq.h_nr_delayed.patch patches/eevdf/WIP/0047-sched-fair-Do-not-try-to-migrate-delayed-dequeue-tas= k.patch <=3D=3D ? patches/eevdf/WIP/0065-sched-Change-ttwu_runnable-vs-sched_delayed.patch patches/eevdf/WIP/0066-sched-Add-ttwu_queue-support-for-delayed-tasks.patch patches/eevdf/WIP/0089-sched-fair-Prevent-negative-lag-increase-during-dela= yed-dequeue.patch <=3D=3D ? -Mike aside: benchmark preemption model sensitivity magnitude poked me in the eye while testing, numbers below in case that's of interest to anyone. preempt=3Dvoluntary rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2566] setting to a 20 second run per stressor stress-ng: info: [2566] dispatching hogs: 4 pipe stress-ng: metrc: [2566] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2566] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2566] pipe 45294217 20.00 22.71 57= .23 2264640.83 566587.74 stress-ng: metrc: [2566] miscellaneous metrics: stress-ng: metrc: [2566] pipe 276.48 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2566] successful run completed in 20.01s rpi5:..debug/sched # echo NO_DELAY_DEQUEUE > features rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2650] setting to a 20 second run per stressor stress-ng: info: [2650] dispatching hogs: 4 pipe stress-ng: metrc: [2650] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2650] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2650] pipe 45379684 20.00 22.69 57= .24 2268917.79 567687.53 stress-ng: metrc: [2650] miscellaneous metrics: stress-ng: metrc: [2650] pipe 276.99 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2650] successful run completed in 20.00s rpi5:..debug/sched # echo DELAY_DEQUEUE > features rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2721] setting to a 20 second run per stressor stress-ng: info: [2721] dispatching hogs: 4 pipe stress-ng: metrc: [2721] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2721] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2721] pipe 45217909 20.00 21.81 58= .13 2260821.48 565698.97 stress-ng: metrc: [2721] miscellaneous metrics: stress-ng: metrc: [2721] pipe 276.00 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2721] successful run completed in 20.00s rpi5:..debug/sched # preempt=3Dlazy rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2070] setting to a 20 second run per stressor stress-ng: info: [2070] dispatching hogs: 4 pipe stress-ng: metrc: [2070] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2070] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2070] pipe 32706095 20.00 17.88 62= .02 1635263.85 409343.56 stress-ng: metrc: [2070] miscellaneous metrics: stress-ng: metrc: [2070] pipe 199.63 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2070] successful run completed in 20.00s rpi5:..debug/sched # echo NO_DELAY_DEQUEUE > features rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2149] setting to a 20 second run per stressor stress-ng: info: [2149] dispatching hogs: 4 pipe stress-ng: metrc: [2149] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2149] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2149] pipe 32226171 20.00 17.93 61= .98 1611264.75 403306.31 stress-ng: metrc: [2149] miscellaneous metrics: stress-ng: metrc: [2149] pipe 196.70 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2149] successful run completed in 20.01s rpi5:..debug/sched # echo DELAY_DEQUEUE > features rpi5:..debug/sched # /usr/bin/stress-ng --pipe 4 --timeout 20s --metrics-br= ief stress-ng: info: [2210] setting to a 20 second run per stressor stress-ng: info: [2210] dispatching hogs: 4 pipe stress-ng: metrc: [2210] stressor bogo ops real time usr time sys t= ime bogo ops/s bogo ops/s stress-ng: metrc: [2210] (secs) (secs) (sec= s) (real time) (usr+sys time) stress-ng: metrc: [2210] pipe 32762333 20.00 18.08 61= .86 1638067.42 409835.28 stress-ng: metrc: [2210] miscellaneous metrics: stress-ng: metrc: [2210] pipe 199.99 MB per sec pipe write = rate (geometic mean of 4 instances) stress-ng: info: [2210] successful run completed in 20.01s =20