From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 381796B42F2 for ; Mon, 26 Nov 2018 12:44:06 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id i55so9559942ede.14 for ; Mon, 26 Nov 2018 09:44:06 -0800 (PST) Received: from outbound-smtp12.blacknight.com (outbound-smtp12.blacknight.com. [46.22.139.17]) by mx.google.com with ESMTPS id 7-v6si609924eji.75.2018.11.26.09.44.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Nov 2018 09:44:04 -0800 (PST) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp12.blacknight.com (Postfix) with ESMTPS id 807171C2E7B for ; Mon, 26 Nov 2018 17:44:04 +0000 (GMT) Date: Mon, 26 Nov 2018 17:44:02 +0000 From: Mel Gorman Subject: Re: Hackbench pipes regression bisected to PSI Message-ID: <20181126174402.GR23260@techsingularity.net> References: <20181126133420.GN23260@techsingularity.net> <20181126160724.GA21268@cmpxchg.org> <20181126165446.GQ23260@techsingularity.net> <20181126173218.GA22640@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20181126173218.GA22640@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Tejun Heo , Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org On Mon, Nov 26, 2018 at 12:32:18PM -0500, Johannes Weiner wrote: > On Mon, Nov 26, 2018 at 04:54:47PM +0000, Mel Gorman wrote: > > On Mon, Nov 26, 2018 at 11:07:24AM -0500, Johannes Weiner wrote: > > > @@ -509,6 +509,15 @@ config PSI > > > > > > Say N if unsure. > > > > > > +config PSI_DEFAULT_DISABLED > > > + bool "Require boot parameter to enable pressure stall information tracking" > > > + default n > > > + depends on PSI > > > + help > > > + If set, pressure stall information tracking will be disabled > > > + per default but can be enabled through passing psi_enable=1 > > > + on the kernel commandline during boot. > > > + > > > endmenu # "CPU/Task time and stats accounting" > > > > > > > Should this default y on the basis that someone only wants the feature if > > they are aware of it? This is not that important as CONFIG_PSI is disabled > > by default and it's up to distribution maintainers to use their brain. > > I went with the NUMA balancing example again here, which defaults to > enabling the feature at boot time. IMO that makes sense, as somebody > would presumably first read through the PSI help text, then decide y > on that before being asked the second question. A "yes, but > " for vendor kernels seems more appropriate than > requiring a double yes for other users to simply get the feature. > That's fair enough. The original NUMA balancing thinking was that it should be enabled because there is a reasonable expectation that it would improve performance regardless of user awareness. PSI is not necessarily the same as it requires a consumer but I accept that a distro maintainer should read the Kconfig text and figure it out. I'll make sure the updated version gets tested, thanks. -- Mel Gorman SUSE Labs