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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A2B5C6FD1C for ; Thu, 23 Mar 2023 07:51:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231327AbjCWHvX (ORCPT ); Thu, 23 Mar 2023 03:51:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45562 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231311AbjCWHvS (ORCPT ); Thu, 23 Mar 2023 03:51:18 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9D4620A10 for ; Thu, 23 Mar 2023 00:51:16 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 3CB2D339C9; Thu, 23 Mar 2023 07:51:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1679557875; h=from:from:reply-to: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=xFRffw+9SvcdtX5CuPeFnJlovLn9+suOg3bbTvNjZ/k=; b=PMZwY6SCQEocvy4dhNouktfWgxmXrsBQGWar+MXVsF+3wdLQAWq/f+cnwsZf1abMaQf6vT 3xAia7Kt3CgmVfx1BMnUnZK4qFTdr5YJNfvZZbTpKEfWM7OkQZUXg7h+gGU3M9lsaWcXEt 9jNm2ZL1edCXAkBy6P9EEMaVRZu4il0= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 199FB132C2; Thu, 23 Mar 2023 07:51:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id iqDPA/MEHGRvDgAAMHmgww (envelope-from ); Thu, 23 Mar 2023 07:51:15 +0000 Date: Thu, 23 Mar 2023 08:51:14 +0100 From: Michal Hocko To: Marcelo Tosatti Cc: Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Russell King , Huacai Chen , Heiko Carstens , x86@kernel.org, Vlastimil Babka Subject: Re: [PATCH v7 00/13] fold per-CPU vmstats remotely Message-ID: References: <20230320180332.102837832@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 22-03-23 11:20:55, Marcelo Tosatti wrote: > On Wed, Mar 22, 2023 at 02:35:20PM +0100, Michal Hocko wrote: [...] > > > "Performance details for the kworker interruption: > > > > > > oslat 1094.456862: sys_mlock(start: 7f7ed0000b60, len: 1000) > > > oslat 1094.456971: workqueue_queue_work: ... function=vmstat_update ... > > > oslat 1094.456974: sched_switch: prev_comm=oslat ... ==> next_comm=kworker/5:1 ... > > > kworker 1094.456978: sched_switch: prev_comm=kworker/5:1 ==> next_comm=oslat ... > > > > > > The example above shows an additional 7us for the > > > > > > oslat -> kworker -> oslat > > > > > > switches. In the case of a virtualized CPU, and the vmstat_update > > > interruption in the host (of a qemu-kvm vcpu), the latency penalty > > > observed in the guest is higher than 50us, violating the acceptable > > > latency threshold for certain applications." > > > > Yes, I have seen that but it doesn't really give a wider context to > > understand why those numbers matter. > > OK. > > "In the case of RAN, a MAC scheduler with TTI=1ms, this causes >100us > interruption observed in a guest (which is above the safety > threshold for this application)." > > Is that OK? This might be a sufficient information for somebody familiar with the matter (not me). So no, not enough. We need to hear a more complete story. -- Michal Hocko SUSE Labs