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 42BF2C77B76 for ; Sun, 23 Apr 2023 01:34:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230039AbjDWBel (ORCPT ); Sat, 22 Apr 2023 21:34:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35406 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229556AbjDWBei (ORCPT ); Sat, 22 Apr 2023 21:34:38 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3862F1FE3 for ; Sat, 22 Apr 2023 18:33:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682213634; 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=09Pqr7rDFYYz3FncrOkQc8pLBhiqcgYn36BtmrtOB5A=; b=RhLuodqJxNfaTAe+b8kflTIseP/rftgKnoDIcwis7LXCnBQ6Q0IL7hy6lzGz10ocnqbesl Q48FEUdijBaHkbOTKkqmmoqTscmaPbNUgma2ktEVYgTRY0oBDN7/+Tna+wivFuSumS8wUR Hh/21aNrCwhvDH6h3jiQPtFAzrJArtw= 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-127-2Xeptx0oPzu-RVqHESuNgw-1; Sat, 22 Apr 2023 21:33:50 -0400 X-MC-Unique: 2Xeptx0oPzu-RVqHESuNgw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BDCFF85A5B1; Sun, 23 Apr 2023 01:33:49 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7FB9F4400C; Sun, 23 Apr 2023 01:33:49 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id CCFF2400DC5BC; Sat, 22 Apr 2023 22:25:01 -0300 (-03) Date: Sat, 22 Apr 2023 22:25:01 -0300 From: Marcelo Tosatti To: Michal Hocko Cc: Andrew Theurer , Andrew Morton , Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , 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> <20230418150200.027528c155853fea8e4f58b2@linux-foundation.org> <98E08059-6607-43FF-84E3-BFF3FF193D09@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 20, 2023 at 09:55:40AM +0200, Michal Hocko wrote: > On Wed 19-04-23 08:44:23, Andrew Theurer wrote: > > > On Apr 19, 2023, at 6:15 AM, Marcelo Tosatti wrote: > > >> Andrew Theurer, can you please explain what problem is the vmstat_work > > >> interruption causing in your testing? > > > > > > +CC Andrew. > > > > Nearly every telco we work with for 5G RAN is demanding <20 usec CPU > > latency as measured by cyclictest & oslat. We cannot achieve under 20 > > usec with the vmstats interruption. > > Are you able to get those latency requirements with PREEMPT_RT? What do you mean, exactly? PREEMPT_RT allows for the preemption of tasks in kernel context (so that higher priority tasks can interrupt lower priority tasks). It also enables IRQ handling to happen in thread context (so that a given thread might be given higher priority than executing a particular IRQ handler). If the question is: "Are you able to achieve <20 usec latency while allowing switching between different tasks ?" The answer with current processor and memory speeds is probably: no. But with more performant processors, you might. However, with a fully isolated processor which does not require switching between tasks, yes you can achieve < 20 usec latency.