From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6AE81C433F5 for ; Wed, 11 May 2022 10:11:37 +0000 (UTC) Received: from localhost ([::1]:45722 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nojJg-0004z7-4z for qemu-devel@archiver.kernel.org; Wed, 11 May 2022 06:11:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51254) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nojIL-00047I-3V for qemu-devel@nongnu.org; Wed, 11 May 2022 06:10:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:35486) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nojIH-0006tl-PD for qemu-devel@nongnu.org; Wed, 11 May 2022 06:10:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652263808; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SVRRkFuVRUEGR8xVM4F38nC6EGwcOpSeHUzVVtWOF3Y=; b=XUb0yyk60zB+fw3uxn6L7P+0lz1F4q7HjXx/3MiXceFsdBWV0JAbzTLWhKB6CaFT+hN6cZ 8ja+C0O74Kn/oPH876ei7O/N7c+n7pcPBKytpLPFuAlkotHoFI/IFpRXYXtoDvb+OC11kS tZ/+R9oew+1WhbrjEcHqcyn7HHJVq8Q= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-480-xI2qkbpxPZ2aFV3s2LhChw-1; Wed, 11 May 2022 06:10:07 -0400 X-MC-Unique: xI2qkbpxPZ2aFV3s2LhChw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2053D805F46 for ; Wed, 11 May 2022 10:10:07 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.142]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2EE251468F31; Wed, 11 May 2022 10:10:05 +0000 (UTC) Date: Wed, 11 May 2022 11:10:03 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: David Hildenbrand Cc: Michal Privoznik , qemu-devel@nongnu.org Subject: Re: [PATCH] util: NUMA aware memory preallocation Message-ID: References: <8a6b84ed-50bc-8f6e-4b71-7e15247c4ac0@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 11, 2022 at 12:03:24PM +0200, David Hildenbrand wrote: > On 11.05.22 11:34, Daniel P. Berrangé wrote: > > On Wed, May 11, 2022 at 11:31:23AM +0200, David Hildenbrand wrote: > >>>> Long story short, management application has no way of learning > >>>> TIDs of allocator threads so it can't make them run NUMA aware. > >>> > >>> This feels like the key issue. The preallocation threads are > >>> invisible to libvirt, regardless of whether we're doing coldplug > >>> or hotplug of memory-backends. Indeed the threads are invisible > >>> to all of QEMU, except the memory backend code. > >>> > >>> Conceptually we need 1 or more explicit worker threads, that we > >>> can assign CPU affinity to, and then QEMU can place jobs on them. > >>> I/O threads serve this role, but limited to blockdev work. We > >>> need a generalization of I/O threads, for arbitrary jobs that > >>> QEMU might want to farm out to specific numa nodes. > >> > >> At least the "-object iothread" thingy can already be used for actions > >> outside of blockdev. virtio-balloon uses one for free page hinting. > > > > Ah that's good to know, so my idea probably isn't so much work as > > I thought it might be. > > I guess we'd have to create a bunch of iothreads on the command line and > then feed them as an array to the memory backend we want to create. We > could then forward the threads to a new variant of os_mem_prealloc(). > > We could > > a) Allocate new iothreads for each memory backend we create. Hm, that > might be suboptimal, we could end up with many iothreads. > > b) Reuse iothreads and have separate sets of iothreads per NUMA node. > Assign them to a node once. > > c) Reuse iothreads and reassign them to NUMA nodes on demand. If all we needs is NUMA affinity, not CPU affinity, then it would be sufficient to create 1 I/O thread per host NUMA node that the VM needs to use. The job running in the I/O can spawn further threads and inherit the NUMA affinity. This might be more clever than it is needed though. I expect creating/deleting I/O threads is cheap in comparison to the work done for preallocation. If libvirt is using -preconfig and object-add to create the memory backend, then we could have option of creating the I/O threads dynamically in -preconfig mode, create the memory backend, and then delete the I/O threads again. > However, I'm not sure what the semantics are when having multiple > backends referencing the iothreads ... Yep, we don't especially need an "ownership" relationship for what we want todo with preallocatino, specially because it is a one off point-in-time usage, not continuous usage as with block devices With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|