From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 C379428134B for ; Thu, 13 Feb 2025 14:27:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739456823; cv=none; b=aFTeJs6T3e+wBCCcnCTeYjYkRmmJqI5lcdQStdM6X85DR3UOwuuW3OniFv+mG1cwXTRRHFw5vZzWHrbXEOjJNYDptfGiBmHSsXOYTdC7fcBAo0+ItCP7lh4eeboVqi0hhGiDek6k2nntGAM95NYYcf8mAnsq9ZiHFNGMN17AQuk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739456823; c=relaxed/simple; bh=v0pVMRWyfNok94km3PUJewnEQHKGogIqu2YvHtUVVMc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QGIHv7PxmehUdJdnVEKSi89lKeRPFEU26M/jhn2mg82LnRoXdF2+I7BK7GgVvrTNSFMouUVV4Ha/FzAG6yynAOu7Vf9F+O4zR58CVWPtE1oarsXgfc7LRQ5hzGpc1OqzSd4//xAAjyNXswDDX5IdVJ/2oekW0N2tAc24Ft7K+5k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none 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=aSoQWpO2; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none 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="aSoQWpO2" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739456820; 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=6M1gDTvPuGgue2fyEVIE80fdtT2TCPvdR21VlIze2TE=; b=aSoQWpO28xS7NzW5hVWkKJikNUdtAUTru/scwQXbPr634BC2sxQwZHNlK5zsbTFmUcp+w6 qyaSCAMlB8I1AiwH6vIXKJw/aBMF0NX+gKbb0SUUBtw+p/JNVhYyDCkhh/PiJWJy+cNL5U SsuPLBjp5YTKYcUJm97152OdSbVDHuU= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-442-Hk1TlQ9bNBO4dF1ASiHtQA-1; Thu, 13 Feb 2025 09:26:59 -0500 X-MC-Unique: Hk1TlQ9bNBO4dF1ASiHtQA-1 X-Mimecast-MFC-AGG-ID: Hk1TlQ9bNBO4dF1ASiHtQA Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 174EE18D95DE; Thu, 13 Feb 2025 14:26:58 +0000 (UTC) Received: from pauld.westford.csb (unknown [10.22.88.188]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 06806180034D; Thu, 13 Feb 2025 14:26:55 +0000 (UTC) Date: Thu, 13 Feb 2025 09:26:53 -0500 From: Phil Auld To: Madadi Vineeth Reddy Cc: Peter Zijlstra , Juri Lelli , Frederic Weisbecker , Waiman Long , linux-kernel@vger.kernel.org Subject: Re: [CHANGE 1/2] sched/isolation: Make use of more than one housekeeping cpu Message-ID: <20250213142653.GA472203@pauld.westford.csb> References: <20250211140104.420739-1-pauld@redhat.com> <4a8d54e7-fa29-4ce4-9023-3cdffa0807e6@linux.ibm.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: <4a8d54e7-fa29-4ce4-9023-3cdffa0807e6@linux.ibm.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On Thu, Feb 13, 2025 at 10:14:04AM +0530 Madadi Vineeth Reddy wrote: > Hi Phil Auld, > > On 11/02/25 19:31, Phil Auld wrote: > > The exising code uses housekeeping_any_cpu() to select a cpu for > > a given housekeeping task. However, this often ends up calling > > cpumask_any_and() which is defined as cpumask_first_and() which has > > the effect of alyways using the first cpu among those available. > > > > The same applies when multiple NUMA nodes are involved. In that > > case the first cpu in the local node is chosen which does provide > > a bit of spreading but with multiple HK cpus per node the same > > issues arise. > > > > Spread the HK work out by having housekeeping_any_cpu() and > > sched_numa_find_closest() use cpumask_any_and_distribute() > > instead of cpumask_any_and(). > > > > Got the overall intent of the patch for better load distribution on > housekeeping tasks. However, one potential drawback could be that by > spreading HK work across multiple CPUs might reduce the time that > some cores can spend in deeper idle states which can be beneficial for > power-sensitive systems. > > Thoughts? NOHZ_full setups are not generally used in power sensitive systems I think. They aren't in our use cases at least. In cases with many cpus a single housekeeping cpu can not keep up. Having other HK cpus in deep idle states while the one in use is overloaded is not a win. If your single HK cpu can keep up then only configure that one HK cpu. The others will go idle and stay there. And since they are nohz_full might get to stay idle even longer. I do have a patch that has this controlled by a sched feature if that is of interest. Then it could be disabled if you don't want it. Cheers, Phil > > Thanks, > Madadi Vineeth Reddy > > > Signed-off-by: Phil Auld > > Cc: Peter Zijlstra > > Cc: Juri Lelli > > Cc: Frederic Weisbecker > > Cc: Waiman Long > > Cc: linux-kernel@vger.kernel.org > > --- > > kernel/sched/isolation.c | 2 +- > > kernel/sched/topology.c | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > > index 81bc8b329ef1..93b038d48900 100644 > > --- a/kernel/sched/isolation.c > > +++ b/kernel/sched/isolation.c > > @@ -40,7 +40,7 @@ int housekeeping_any_cpu(enum hk_type type) > > if (cpu < nr_cpu_ids) > > return cpu; > > > > - cpu = cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask); > > + cpu = cpumask_any_and_distribute(housekeeping.cpumasks[type], cpu_online_mask); > > if (likely(cpu < nr_cpu_ids)) > > return cpu; > > /* > > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > > index c49aea8c1025..94133f843485 100644 > > --- a/kernel/sched/topology.c > > +++ b/kernel/sched/topology.c > > @@ -2101,7 +2101,7 @@ int sched_numa_find_closest(const struct cpumask *cpus, int cpu) > > for (i = 0; i < sched_domains_numa_levels; i++) { > > if (!masks[i][j]) > > break; > > - cpu = cpumask_any_and(cpus, masks[i][j]); > > + cpu = cpumask_any_and_distribute(cpus, masks[i][j]); > > if (cpu < nr_cpu_ids) { > > found = cpu; > > break; > --