From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) by kanga.kvack.org (Postfix) with ESMTP id 9B6CB6B000D for ; Thu, 19 Jul 2018 09:18:44 -0400 (EDT) Received: by mail-pg1-f197.google.com with SMTP id 132-v6so3613186pga.18 for ; Thu, 19 Jul 2018 06:18:44 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id d9-v6si5344738pll.255.2018.07.19.06.18.43 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 19 Jul 2018 06:18:43 -0700 (PDT) Date: Thu, 19 Jul 2018 15:18:36 +0200 From: Peter Zijlstra Subject: Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO Message-ID: <20180719131836.GG2476@hirez.programming.kicks-ass.net> References: <20180712172942.10094-1-hannes@cmpxchg.org> <20180712172942.10094-9-hannes@cmpxchg.org> <20180718120318.GC2476@hirez.programming.kicks-ass.net> <20180719092614.GY2512@hirez.programming.kicks-ass.net> <20180719125038.GB13799@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180719125038.GB13799@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Ingo Molnar , Andrew Morton , Linus Torvalds , Tejun Heo , Suren Baghdasaryan , Vinayak Menon , Christopher Lameter , Mike Galbraith , Shakeel Butt , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Arnaldo Carvalho de Melo On Thu, Jul 19, 2018 at 08:50:38AM -0400, Johannes Weiner wrote: > On Thu, Jul 19, 2018 at 11:26:14AM +0200, Peter Zijlstra wrote: > > On Wed, Jul 18, 2018 at 02:03:18PM +0200, Peter Zijlstra wrote: > > > > > Leaving us just 5 bytes short of needing a single cacheline :/ > > > > > > struct ponies { > > > unsigned int tasks[3]; /* 0 12 */ > > > unsigned int cpu_state:2; /* 12:30 4 */ > > > unsigned int io_state:2; /* 12:28 4 */ > > > unsigned int mem_state:2; /* 12:26 4 */ > > > > > > /* XXX 26 bits hole, try to pack */ > > > > > > /* typedef u64 */ long long unsigned int last_time; /* 16 8 */ > > > /* typedef u64 */ long long unsigned int some_time[3]; /* 24 24 */ > > > /* typedef u64 */ long long unsigned int full_time[2]; /* 48 16 */ > > > /* --- cacheline 1 boundary (64 bytes) --- */ > > > /* typedef u64 */ long long unsigned int nonidle_time; /* 64 8 */ > > > > > > /* size: 72, cachelines: 2, members: 8 */ > > > /* bit holes: 1, sum bit holes: 26 bits */ > > > /* last cacheline: 8 bytes */ > > > }; > > > > > > ARGGH! > > > > It _might_ be possible to use curr->se.exec_start for last_time if you > > very carefully audit and place the hooks. I've not gone through it in > > detail, but it might just work. > > Hnngg, and chop off an entire cacheline... Yes.. a worthy goal :-) > But don't we flush that delta out and update the timestamp on every > tick? Indeed. > entity_tick() does update_curr(). That might be too expensive :( Well, since you already do all this accounting on every enqueue/dequeue, this can run many thousands of times per tick already, so once per tick doesn't sound bad. However, I just realized this might not in fact work, because curr->se.exec_start is per task, and you really want something per-cpu for this. Bah, if only perf had a useful tool to report on data layout instead of this c2c crap.. :-( The thinking being that we could maybe find a usage-hole (a data member that is not in fact used) near something we already touch for writing.