From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from m16.mail.163.com (m16.mail.163.com [117.135.210.3]) (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 505143DBD7E for ; Fri, 10 Apr 2026 16:39:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=117.135.210.3 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775839200; cv=none; b=rfYDiv74KnNxuto/Am199tjFgBrJLb5JnsZYfhdhA4q+AA+MzrjKynRtetCdsY3BVuzkBRGDZREBpCi+Ft2T2Cin4IuQXutXKXvjwCH+AHIGXnHX6c1KmhYRHf6rdPkRfJUkNUBQSaK+VvTwHLO+nK+y2qO2PldR32ofOzyLwXI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775839200; c=relaxed/simple; bh=kl/eskVOL8eNVtwEL6cwqUUmNHBy7QNZtfYQT23LVhU=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-Id: Content-Type:MIME-Version; b=QENUTIlhjpi3F8qJ4rZ2hJwYAgZPciqdCN6QSDvFWUJf93IXRU7L0tK1LHaSZ/LXKKq3y0LOPM8rmnn/bVbXRwrAxaMDb/hcD4j6SzyY4OyDrLNrHgBFW+kZPowqNpQ47JwosswFVUxFjkuG6wij6UFdionN61T+JNoTbNaVj0M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=Q1HiBhNS; arc=none smtp.client-ip=117.135.210.3 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="Q1HiBhNS" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-Id:Content-Type: MIME-Version; bh=/hBGszhyGIxn0ubN7uN6171O4/vIt8IbKfG13KLWvi4=; b=Q1HiBhNSp8DNaWB8TEoJ6VAcFkafqvsd3atMCQeSE+jGW9eQpmA7uwPKsfE7e2 a4rB2i+vFeNEnwpFTqJxa18A6+pzS4fqCSwE26WVvWzuq5ZJZk1CpM7fpPEmtWFF 9wd5GtnpSurcgeCY6lwla6m8iWTVTA9jqkYHiBZV1dU4k= Received: from 229.199.16.172.in-addr.arpa (unknown []) by gzga-smtp-mtada-g1-2 (Coremail) with SMTP id _____wDXh7_OJ9lpXmSdEQ--.58972S2; Sat, 11 Apr 2026 00:39:46 +0800 (CST) From: Cao Ruichuang To: Juri Lelli 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 In-Reply-To: References: Date: Sat, 11 Apr 2026 00:39:41 +0800 Message-Id: <177583918187.65608.81441247578852229@163.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID:_____wDXh7_OJ9lpXmSdEQ--.58972S2 X-Coremail-Antispam: 1Uf129KBjvdXoWrtr4kAr1Dtw48ZFW5Cr47CFg_yoWDCFb_WF Wvq34kCr1DCFyYvr1Ikr43JrZ2qayrGFyUuw48WF42yrWkJan5AFZ8ZF93GFn3C393CFnx WFn7XrWI9w1F9jkaLaAFLSUrUUUUjb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUvcSsGvfC2KfnxnUUI43ZEXa7xRl1v-3UUUUU== X-CM-SenderInfo: pfuht3jhqyimi6rwjhhfrp/xtbC6BLOCGnZJ9LN8wAA3H 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. Thanks, Cao Ruichuang