From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 189113CF690 for ; Fri, 24 Apr 2026 12:38:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777034294; cv=none; b=Ot9MO5G+Rm2tEtpkfdfzT5tAYNeqzpXlRVwqQ23RzYL1PzWE4A6GYQOplZ1dC3W2hJlc/TMN0GItplHkwA3QE535s/jTlLa4jSp092MfA6FJno+tUsVOMlAVkMLVkSE6xv/r04mEDDaSoCJulNnhNzO7VqWTtkI3xKeEjwe7g6w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777034294; c=relaxed/simple; bh=qF6XRnXlc1U1jANpDymnx4vAAI3XWN648dg5/Nwnu8s=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WPr50ReK98GZgWsrPXArCuHJqTx9QYskcrYNEvuHjPzqqmBho2zWXeJrYaWXAGPxMfEClVqstTDmh7SBxMQAomsmbQU0E0tP/6vQGp2nTLgwhVCHf/iQfheOo9zTGIM2nTov6EDiGgKMW+L/QzI4WEvIf7AhZC4hwIa4BS+QQdk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=QniOdeJ7; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=SIDbSd3D; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QniOdeJ7"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="SIDbSd3D" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1777034289; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qc9obRF8JCoxbvB4GvC2UWIw9W8oUUv7NLmDu5yIJxM=; b=QniOdeJ7yyy89XmRP6EpcYR81Ge31rdw5+yhHnZ+rI6pergc0m0sQYcuyJPhUCEByQJZPZ +rFzaiPxN5ShI8O0v4RnkYgEEH1TkWXa0o6wCoday8u9D/VjTq5I7ebPBN7LvAD6FH+W5z gT54Ddyqm7w/zIPnSNUvjPfS1ITi6uc= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-357-FjpSgin1ONOZFCyy1Masqg-1; Fri, 24 Apr 2026 08:38:07 -0400 X-MC-Unique: FjpSgin1ONOZFCyy1Masqg-1 X-Mimecast-MFC-AGG-ID: FjpSgin1ONOZFCyy1Masqg_1777034286 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-43d03065782so5102722f8f.0 for ; Fri, 24 Apr 2026 05:38:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1777034286; x=1777639086; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=qc9obRF8JCoxbvB4GvC2UWIw9W8oUUv7NLmDu5yIJxM=; b=SIDbSd3DucznQn/+z6VhrtGsMnkag00vN9sD7z+HH2v/fniuukqEdBU8wn5WxWS2j/ BiFUMq+JDsQmBXTygsIDUUKJL3v1gv6w1TqVfjONKwGcHPh3wudtkmNys56CXxN5+S6B BFMzXZ1Q4hIRWpxyw1YCyjw4g+aiTXJF9vsDOlY0wnxdXev9mrch47orQG19XFOwcfxF TRXBwb+VQqDPwtd66Su99vQhCEyB1PCb/7f7S/mrxEW8ZTcdGOFQZhJ5YM+eEMfkkIwW kVwb8vJwwWuBc3mPVed91atTGH3apt9cdjEwcwm383eAyHhZSzWg9S2Zk2tGhH1mhr3R y13A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777034286; x=1777639086; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=qc9obRF8JCoxbvB4GvC2UWIw9W8oUUv7NLmDu5yIJxM=; b=RXFPyii0NKhXpNmgqD3B9VhDzlxi8F1RzhpVQPhRu0d4m4eGpYq+JCaAYvwrnPoh1U oMktI52LCJ0Z1xbZNzV9FpX/pdBm2knFfH7bO5TThUR7hFVfwZWAxWSdSHvnDXHWIci6 gQNhA0Xq1NHRx0S2yEUZTLsbpwlVS3fMNs5UdDvMpUNJPYxsNPNQYaxZrst0p/B60P6/ v6euF3ObzueHDMMEfedTipw7vhrQEQeL9bCHiUQn/ctd7fjkBVV2IprMoKAWU6xbmK/s QX6p5AmIjibMo5TLqz8draBTknhNDUK6pZg2cW3gqlAWpjx2NQ14do44mxo6aoOgPK5h dRYw== X-Gm-Message-State: AOJu0YzlhdDEjcAOW2VzwsvdvClrdkbM/sYRjzgYpfrJgP67ec3E9YQS +pTGmqWhsqGwStER9acWxz7BQdfpWeDwItHqLNR7kIBnZh9eybAlYwwnYWStsaEImGBWp7ZIW7n 2aKVTyr14cxQliyXeBF5LhAufs/Cfa1LNicokqzRHXpxRJYSULF2P2hGzIEdvwwetvw== X-Gm-Gg: AeBDiesQ1pdh0cipPNpNBT4HZ/NxUtCVLDMVx6lpnxS0yTm5K/fL0CvGRU3AEP5p1Rz Rv8drDmZ9h3obKBEdIo623kxfM5Pl5Qpq/nAtwpt3G0S3HL2eifXH1NQxFAc47iC82mfTBknbQS FXg1MTqvrIClPXBUKXfzxp98O16ds89hhcB+LWCM8ShQ4/UBJiPZA8QSzq2fEaI0t892ffUsJ6w NRycKeUP1OxXiGMY6PpswpnoLYfaGRGf7kNtGHezvhYhzsACa74AsIRbfAxyJIAOv97xMgOdgjq tlzBrdPaW9VX/O1T/LzFyy8cbC0KWCaJaEm23R7Cr63ePnVPkNyj9U7MjTCQFNZ40cLI6x7ellc /qqYD8MULgvObyyj3HJp5tFpZrxpgQOfUS899b+0dTUBMHIuWmqisV5VyQrourw== X-Received: by 2002:a05:600c:3b11:b0:48a:525b:e148 with SMTP id 5b1f17b1804b1-48a525be2f8mr252547935e9.4.1777034286267; Fri, 24 Apr 2026 05:38:06 -0700 (PDT) X-Received: by 2002:a05:600c:3b11:b0:48a:525b:e148 with SMTP id 5b1f17b1804b1-48a525be2f8mr252547635e9.4.1777034285800; Fri, 24 Apr 2026 05:38:05 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.7.99]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fc10019bsm601438225e9.4.2026.04.24.05.38.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Apr 2026 05:38:04 -0700 (PDT) Date: Fri, 24 Apr 2026 14:38:02 +0200 From: Juri Lelli To: Cao Ruichuang Cc: linux-kernel@vger.kernel.org Subject: Re: Kernel 6.14.11 dl_server_timer(...) causing IPI/Function Call Interrupts on isolcpu/nohz_full cores, performance regression Message-ID: References: <177583918187.65608.81441247578852229@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <177583918187.65608.81441247578852229@163.com> Hello, On 11/04/26 00:39, Cao Ruichuang wrote: > Hi Juri, > > I tested the "sched/deadline: Make dl-server nohz full aware" change > shape from f237e524f3c7 on the current mainline tree in a minimal QEMU > setup. > > I used a latest-tree tiny x86 kernel with: > > nohz_full=1 isolcpus=domain,managed_irq,1 irqaffinity=0 rcu_nocbs=1 > > and a CPU1-pinned busy loop as the only user workload. To observe the > periodic activity, I installed a kprobe on start_dl_timer and counted > hits over the same 5 second window. > > On the unmodified tree, I consistently saw: > > START_DL_TIMER_COUNT=118 > > With the sched_can_stop_tick() change from f237e524f3c7 applied, I saw: > > START_DL_TIMER_COUNT=20 > START_DL_TIMER_COUNT=22 > > So on current mainline this still looks like a real improvement in the > same direction David reported earlier: the periodic dl-server activity > is reduced substantially, although it is not eliminated completely in my > QEMU setup. > > I am not sending this as a patch, only as an extra data point in favor > of that fix direction on a latest-tree test setup. Right. I also managed to reproduce again on mainline. The actual difference from when I first start looking at this is that the "one per second" dl-server period timer gets handled (and reprogrammed) on housekeeping CPUs in my test setting (vng), which doesn't thus interrupt the isolated busy workload, but it still seems useless. In the meantime we added dl-server for scx as well, so my first attempt gets a little uglier when trying to take that into account and I will need more time to try and see if I can come up with something better. Thanks, Juri