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 X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A36C9C606BD for ; Mon, 8 Jul 2019 16:30:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6FA1F21537 for ; Mon, 8 Jul 2019 16:30:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="vCUqTPl2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733060AbfGHQa3 (ORCPT ); Mon, 8 Jul 2019 12:30:29 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:44486 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728834AbfGHQa2 (ORCPT ); Mon, 8 Jul 2019 12:30:28 -0400 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=04VsQin5fQQD6HrGTvlUwJ6xlZUOLvn+UaWNLc/zkB0=; b=vCUqTPl2ipzmd49ySsSXpS65M eXeYC3nfJ/AjlLrdFTNrvfm6qaY6inXl3PWVbhn9hO92uioXOG3N8I6wMhs0Zi89HITX8AdcZ255l RuMAYwE5LSqd9zGZLXua2w3KlVMxL62qsbvHtyWHJKQe7G/T7vbwOFzUovis0sVtMYL1y80d5p6Qq QlnkSt5rwGGu9em8SB3D0qfIAfz+HkTJaEjeDULOAFkGsxbJqhkoY73kK36/TEjF7vTOdx1EDgG1w 3YNgyJQg1elhAxBsv8HtJdRiZrz8CWvd7HiYsEPUT3EFrXtMkceI6mTndjmTswwc8A06ozJRK+bmw 090eYDW4g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hkWX1-0007rA-5M; Mon, 08 Jul 2019 16:30:25 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8559420976EFB; Mon, 8 Jul 2019 18:30:21 +0200 (CEST) Date: Mon, 8 Jul 2019 18:30:21 +0200 From: Peter Zijlstra To: Ian Rogers Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-kernel@vger.kernel.org, Kan Liang , Stephane Eranian Subject: Re: [PATCH 3/7] perf: order iterators for visit_groups_merge into a min-heap Message-ID: <20190708163021.GG3419@hirez.programming.kicks-ass.net> References: <20190702065955.165738-1-irogers@google.com> <20190702065955.165738-4-irogers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190702065955.165738-4-irogers@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 01, 2019 at 11:59:51PM -0700, Ian Rogers wrote: > The groups rbtree holding perf events, either for a CPU or a task, needs > to have multiple iterators that visit events in group_index (insertion) > order. Rather than linearly searching the iterators, use a min-heap to go > from a O(#iterators) search to a O(log2(#iterators)) insert cost per event > visited. Is this actually faster for the common (very small n) case? ISTR 'stupid' sorting algorithms are actually faster when the data fits into L1 > Signed-off-by: Ian Rogers > --- > kernel/events/core.c | 123 +++++++++++++++++++++++++++++++++---------- > 1 file changed, 95 insertions(+), 28 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 9a2ad34184b8..396b5ac6dcd4 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -3318,6 +3318,77 @@ static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx, > ctx_sched_out(&cpuctx->ctx, cpuctx, event_type); > } > > +/* Data structure used to hold a min-heap, ordered by group_index, of a fixed > + * maximum size. > + */ Broken comment style. > +struct perf_event_heap { > + struct perf_event **storage; > + int num_elements; > + int max_elements; > +}; > + > +static void min_heap_swap(struct perf_event_heap *heap, > + int pos1, int pos2) > +{ > + struct perf_event *tmp = heap->storage[pos1]; > + > + heap->storage[pos1] = heap->storage[pos2]; > + heap->storage[pos2] = tmp; > +} > + > +/* Sift the perf_event at pos down the heap. */ > +static void min_heapify(struct perf_event_heap *heap, int pos) > +{ > + int left_child, right_child; > + > + while (pos > heap->num_elements / 2) { > + left_child = pos * 2; > + right_child = pos * 2 + 1; > + if (heap->storage[pos]->group_index > > + heap->storage[left_child]->group_index) { > + min_heap_swap(heap, pos, left_child); > + pos = left_child; > + } else if (heap->storage[pos]->group_index > > + heap->storage[right_child]->group_index) { > + min_heap_swap(heap, pos, right_child); > + pos = right_child; > + } else { > + break; > + } > + } > +} > + > +/* Floyd's approach to heapification that is O(n). */ > +static void min_heapify_all(struct perf_event_heap *heap) > +{ > + int i; > + > + for (i = heap->num_elements / 2; i > 0; i--) > + min_heapify(heap, i); > +} > + > +/* Remove minimum element from the heap. */ > +static void min_heap_pop(struct perf_event_heap *heap) > +{ > + WARN_ONCE(heap->num_elements <= 0, "Popping an empty heap"); > + heap->num_elements--; > + heap->storage[0] = heap->storage[heap->num_elements]; > + min_heapify(heap, 0); > +} Is this really the first heap implementation in the kernel? > @@ -3378,12 +3453,14 @@ static int visit_groups_merge(struct perf_event_context *ctx, > struct cgroup_subsys_state *css; > > for (css = &cpuctx->cgrp->css; css; css = css->parent) { > - itrs[num_itrs] = perf_event_groups_first(groups, > + heap.storage[heap.num_elements] = > + perf_event_groups_first(groups, > cpu, > css->cgroup); > - if (itrs[num_itrs]) { > - num_itrs++; > - if (num_itrs == max_itrs) { > + if (heap.storage[heap.num_elements]) { > + heap.num_elements++; > + if (heap.num_elements == > + heap.max_elements) { > WARN_ONCE( > max_cgroups_with_events_depth, > "Insufficient iterators for cgroup depth"); That's turning into unreadable garbage due to indentation; surely there's a solution for that.