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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0CF3C433F5 for ; Tue, 5 Oct 2021 14:13:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8151E6113A for ; Tue, 5 Oct 2021 14:13:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236367AbhJEOPk (ORCPT ); Tue, 5 Oct 2021 10:15:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:48278 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236157AbhJEOOW (ORCPT ); Tue, 5 Oct 2021 10:14:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633443151; 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=xdwRgKHT2YQyjAMlBxShEGrwGI1C4pMFWXSUBFxhHNA=; b=Q7IxkZVIamxOwV/Woax/mmT9diZgtidMOoHz7moeR5MsI683m9Fvy7xG/5Wmsn1kKD31uK Qteta8uYpUDqhjmPzDp80SkR7qSdVmCInBmwZOoQuOSm2Hj/dTfGg6XrkO1GItnF7EoeLh FCvPGKZfNHJvmDRBC/cCnmcEwbcP8sg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-330-sFGoP4hRPaO-vNKgLVXCXQ-1; Tue, 05 Oct 2021 10:12:17 -0400 X-MC-Unique: sFGoP4hRPaO-vNKgLVXCXQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A1919100D680; Tue, 5 Oct 2021 14:12:15 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.16.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 011315F4EB; Tue, 5 Oct 2021 14:12:13 +0000 (UTC) Date: Tue, 5 Oct 2021 10:12:12 -0400 From: Phil Auld To: Peter Zijlstra Cc: Vincent Guittot , Mike Galbraith , Mel Gorman , Ingo Molnar , Valentin Schneider , Aubrey Li , Barry Song , Srikar Dronamraju , LKML Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running Message-ID: References: <20210922132002.GX3959@techsingularity.net> <20210922150457.GA3959@techsingularity.net> <20210922173853.GB3959@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 05, 2021 at 12:36:22PM +0200 Peter Zijlstra wrote: > On Thu, Sep 23, 2021 at 08:24:03AM -0400, Phil Auld wrote: > > > It's capped at 8 cpus, which is pretty easy to reach these days, so the > > values don't get too large. That scaling is almost a no-op these days. > > https://lkml.kernel.org/r/YVwdrh5pg0zSv2/b@hirez.programming.kicks-ass.net > > Ooh, hey, we already fixed that :-) > Thanks Peter. I'm always a little behind upstream (nature of the job :) That link leads to a message Id not found. But from what I can see the code that takes the min of online cpus and 8 is still present. > So the reasoning there is that if the values get too big, interactiviy > get *really* bad, but if you go from say 1 to 4 CPUs, interactivity can > improve due to being able to run on other CPUs. > > At 8 CPUs we end up at 6ms*4=24ms, which is already pretty terrible. > And actually you mention the same thing later on. Most systems, even desktops, have 8+ cpus these days so the scaling is mostly not doing anything except multiplying by 4, right? So no-op was not the right way to describe it maybe. But it's not getting bigger with larger numbers of cpus beyond a pretty commonly reached limit. Cheers, Phil --