From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO Date: Thu, 19 Jul 2018 15:18:36 +0200 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 Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=cc72GVGe+gKbKerlxDkv31VhiqymTnnXhleURTpZrpM=; b=tBRQS7fKILX5iFNGRWVefIvYj OjHyoA0Gt2+xhfCm1oAvHgzPBozsDlVIMLblTXX3AVdnxhzJ1Fd70X1mQn+1pONgletaYfwq9zhGV ZxcodwZXwkbXLyQ8zlhwoI99bbOe0VN5+ucBNwzY1Yr8IlagXbVSsIzvtL7vGMDzf94edgykOqLgL fl/c7k2czebmE0KDBWpHZNUCSJTtNxUsXh01TtdrIbYMGbFy9g8LFLMtsZQznG3jpfjl73StwhFoV Oau2kEG5mmlvsl04cBr+KSc5EOIKTDyXbCdwG64FvGfihf+wXdEzjvtkPO9Auw7h8Dvc3HiobQqFz Content-Disposition: inline In-Reply-To: <20180719125038.GB13799@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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.