From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752078AbdHCUaU (ORCPT ); Thu, 3 Aug 2017 16:30:20 -0400 Received: from mga02.intel.com ([134.134.136.20]:35889 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752052AbdHCUaR (ORCPT ); Thu, 3 Aug 2017 16:30:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,317,1498546800"; d="scan'208";a="135830168" Subject: Re: [PATCH v6 1/3] perf/core: use rb trees for pinned/flexible groups To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Andi Kleen , Kan Liang , Dmitri Prokhorov , Valery Cherepennikov , Mark Rutland , Stephane Eranian , David Carrillo-Cisneros , linux-kernel References: <96c7776f-1f17-a39e-23e9-658596216d6b@linux.intel.com> <20170803130002.oatczvnaalplrsep@hirez.programming.kicks-ass.net> From: Alexey Budankov Organization: Intel Corp. Message-ID: <86cbe0b0-a1ec-4d5f-addc-87bccf2e97d7@linux.intel.com> Date: Thu, 3 Aug 2017 23:30:09 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170803130002.oatczvnaalplrsep@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.08.2017 16:00, Peter Zijlstra wrote: > On Wed, Aug 02, 2017 at 11:13:54AM +0300, Alexey Budankov wrote: >> This patch moves event groups into rb tree sorted by CPU, so that >> multiplexing hrtimer interrupt handler would be able skipping to the current >> CPU's list and ignore groups allocated for the other CPUs. >> >> New API for manipulating event groups in the trees is implemented as well >> as adoption on the API in the current implementation. >> >> Because perf_event_groups_iterate() API provides capability to execute >> a callback for every event group in a tree, adoption of the API introduces >> some code that packs and unpacks arguments of functions existing in >> the implementation as well as adjustments of their calling signatures >> e.g. ctx_pinned_sched_in(), ctx_flexible_sched_in() and inherit_task_group(). > > This does not speak of why we need group_list. > >> Signed-off-by: Alexey Budankov >> --- >> include/linux/perf_event.h | 18 ++- >> kernel/events/core.c | 389 +++++++++++++++++++++++++++++++++------------ >> 2 files changed, 306 insertions(+), 101 deletions(-) >> >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >> index a3b873f..282f121 100644 >> --- a/include/linux/perf_event.h >> +++ b/include/linux/perf_event.h >> @@ -572,6 +572,20 @@ struct perf_event { >> */ >> struct list_head group_entry; >> struct list_head sibling_list; >> + /* >> + * Node on the pinned or flexible tree located at the event context; >> + * the node may be empty in case its event is not directly attached >> + * to the tree but to group_list list of the event directly >> + * attached to the tree; >> + */ >> + struct rb_node group_node; >> + /* >> + * List keeps groups allocated for the same cpu; >> + * the list may be empty in case its event is not directly >> + * attached to the tree but to group_list list of the event directly >> + * attached to the tree; >> + */ >> + struct list_head group_list; >> >> /* >> * We need storage to track the entries in perf_pmu_migrate_context; we >> @@ -741,8 +755,8 @@ struct perf_event_context { >> struct mutex mutex; >> >> struct list_head active_ctx_list; >> - struct list_head pinned_groups; >> - struct list_head flexible_groups; >> + struct rb_root pinned_groups; >> + struct rb_root flexible_groups; >> struct list_head event_list; >> int nr_events; >> int nr_active; >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index 426c2ff..0a4f619 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -1466,8 +1466,12 @@ static enum event_type_t get_event_type(struct perf_event *event) >> return event_type; >> } >> >> -static struct list_head * >> -ctx_group_list(struct perf_event *event, struct perf_event_context *ctx) >> +/* >> + * Extract pinned or flexible groups from the context >> + * based on event attrs bits; >> + */ >> +static struct rb_root * >> +get_event_groups(struct perf_event *event, struct perf_event_context *ctx) >> { >> if (event->attr.pinned) >> return &ctx->pinned_groups; >> @@ -1475,6 +1479,160 @@ ctx_group_list(struct perf_event *event, struct perf_event_context *ctx) >> return &ctx->flexible_groups; >> } >> >> +static void >> +perf_event_groups_insert(struct rb_root *groups, >> + struct perf_event *event); >> + >> +static void >> +perf_event_groups_delete(struct rb_root *groups, >> + struct perf_event *event); > > Can't we do away with these fwd declarations by simple reordering of the > function definitions? Ok. I will clean this up. > >> +/* >> + * Helper function to insert event into the pinned or >> + * flexible groups; >> + */ >> +static void >> +add_event_to_groups(struct perf_event *event, struct perf_event_context *ctx) >> +{ >> + struct rb_root *groups; >> + >> + groups = get_event_groups(event, ctx); >> + perf_event_groups_insert(groups, event); >> +} >> + >> +/* >> + * Helper function to delete event from its groups; >> + */ >> +static void >> +del_event_from_groups(struct perf_event *event, struct perf_event_context *ctx) >> +{ >> + struct rb_root *groups; >> + >> + groups = get_event_groups(event, ctx); >> + perf_event_groups_delete(groups, event); >> +} >> + >> +/* >> + * Insert a group into a tree using event->cpu as a key. If event->cpu node >> + * is already attached to the tree then the event is added to the attached >> + * group's group_list list. >> + */ >> +static void >> +perf_event_groups_insert(struct rb_root *groups, >> + struct perf_event *event) >> +{ >> + struct rb_node **node; >> + struct rb_node *parent; >> + struct perf_event *node_event; >> + >> + node = &groups->rb_node; >> + parent = *node; >> + >> + while (*node) { >> + parent = *node; >> + node_event = container_of(*node, >> + struct perf_event, group_node); >> + >> + if (event->cpu < node_event->cpu) { >> + node = &parent->rb_left; >> + } else if (event->cpu > node_event->cpu) { >> + node = &parent->rb_right; > > I would much prefer you use a comparator like: Ok. I Will do. > > static always_inline int > perf_event_less(struct perf_event *left, struct perf_event *right) > { > if (left->cpu < right_cpu) > return 1; > > return 0; > } > > That way we can add additional order. In specific ARM also wants things > ordered on PMU for their big.LITTLE stuff. > >> + } else { >> + list_add_tail(&event->group_entry, >> + &node_event->group_list); >> + return; > > Urgh, so this is what you want that list for... why not keep duplicates > in the tree itself and iterate that? > >> + } >> + } >> + >> + list_add_tail(&event->group_entry, &event->group_list); >> + >> + rb_link_node(&event->group_node, parent, node); >> + rb_insert_color(&event->group_node, groups); >> +} > >> +/* >> + * Find group list by a cpu key and rotate it. >> + */ >> +static void >> +perf_event_groups_rotate(struct rb_root *groups, int cpu) >> +{ >> + struct rb_node *node; >> + struct perf_event *node_event; >> + >> + node = groups->rb_node; >> + >> + while (node) { >> + node_event = container_of(node, >> + struct perf_event, group_node); >> + >> + if (cpu < node_event->cpu) { >> + node = node->rb_left; >> + } else if (cpu > node_event->cpu) { >> + node = node->rb_right; >> + } else { >> + list_rotate_left(&node_event->group_list); >> + break; >> + } >> + } >> +} > > Ah, you worry about how to rotate inside a tree? Exactly. > > You can do that by adding (run)time based ordering, and you'll end up > with a runtime based scheduler. Do you mean replacing a CPU indexed rb_tree of lists with an CPU indexed rb_tree of counter indexed rb_trees? > > A trivial variant keeps a simple counter per tree that is incremented > for each rotation. That should end up with the events ordered exactly > like the list. And if you have that comparator like above, expressing > that additional ordering becomes simple ;-) > > Something like: > > struct group { > u64 vtime; > rb_tree tree; > }; > > bool event_less(left, right) > { > if (left->cpu < right->cpu) > return true; > > if (left->cpu > right_cpu) > return false; > > if (left->vtime < right->vtime) > return true; > > return false; > } > > insert_group(group, event, tail) > { > if (tail) > event->vtime = ++group->vtime; > > tree_insert(&group->root, event); > } > > Then every time you use insert_group(.tail=1) it goes to the end of that > CPU's 'list'. > Could you elaborate more on how to implement rotation? Do you mean the rotation of rb_tree? So that the iteration order of the counter indexed rb_tree would coincide with iteration order of a list after rotation? And I then still need struct rb_tree group_tree in perf_event structure: + /* + * Node on the pinned or flexible tree located at the event context; + * the node may be empty in case its event is not directly attached + * to the tree but to group_list list of the event directly + * attached to the tree; + */ + struct rb_node group_node; + /* + * List keeps groups allocated for the same cpu; + * the list may be empty in case its event is not directly + * attached to the tree but to group_list list of the event directly + * attached to the tree; + */ + struct rb_tree group_tree; > > The added benefit is that it then becomes fairly simple to improve upon > the RR scheduling, which suffers a bunch of boundary conditions where > the task runtimes mis-align with the rotation window. > >> +typedef int(*perf_event_groups_iterate_f)(struct perf_event *, void *); > > We already have perf_iterate_f, the only difference appears to be that > this has a return value. Surely these can be unified. Ok. I will unify at some point. > >> +/* >> + * Iterate event groups and call provided callback for every group in the tree. >> + * Iteration stops if the callback returns non zero. >> + */ >> +static int >> +perf_event_groups_iterate(struct rb_root *groups, >> + perf_event_groups_iterate_f callback, void *data) >> +{ >> + int ret = 0; >> + struct rb_node *node; >> + struct perf_event *node_event, *event; > > In general we prefer variable definitions to be ordered on line length, > longest first. So the exact opposite of what you have here. Accepted. > >> + >> + for (node = rb_first(groups); node; node = rb_next(node)) { >> + node_event = container_of(node, struct perf_event, group_node); >> + list_for_each_entry(event, &node_event->group_list, >> + group_entry) { >> + ret = callback(event, data); >> + if (ret) { >> + return ret; >> + } >> + } >> + } >> + >> + return ret; >> +} >> + >> /* >> * Add a event from the lists for its context. >> * Must be called with ctx->mutex and ctx->lock held. > >> @@ -1869,6 +2023,22 @@ group_sched_out(struct perf_event *group_event, >> cpuctx->exclusive = 0; >> } >> >> +struct group_sched_params { >> + struct perf_cpu_context *cpuctx; >> + struct perf_event_context *ctx; >> + int can_add_hw; >> +}; >> + >> +static int >> +group_sched_out_callback(struct perf_event *event, void *data) >> +{ >> + struct group_sched_params *params = data; >> + >> + group_sched_out(event, params->cpuctx, params->ctx); >> + >> + return 0; >> +} > > Right, C sucks.. or possibly you've chosen the wrong pattern. Consequences of new API integration with a callback in signature :) > > So the alternative is something like: > > #define for_each_group_event(event, group, cpu, pmu, field) \ > for (event = rb_entry_safe(group_first(group, cpu, pmu),\ > typeof(*event), field); \ > event && event->cpu == cpu && event->pmu == pmu; \ > event = rb_entry_safe(rb_next(&event->field), \ > typeof(*event), field)) > > > And then you can write things like: > > for_each_group_event(event, group, cpu, pmu) > group_sched_out(event, cpuctx, ctx); > > >> + >> #define DETACH_GROUP 0x01UL >> >> /* >> @@ -2712,7 +2882,10 @@ static void ctx_sched_out(struct perf_event_context *ctx, >> enum event_type_t event_type) >> { >> int is_active = ctx->is_active; >> - struct perf_event *event; >> + struct group_sched_params params = { >> + .cpuctx = cpuctx, >> + .ctx = ctx >> + }; >> >> lockdep_assert_held(&ctx->lock); >> >> @@ -2759,13 +2932,13 @@ static void ctx_sched_out(struct perf_event_context *ctx, >> >> perf_pmu_disable(ctx->pmu); >> if (is_active & EVENT_PINNED) { >> - list_for_each_entry(event, &ctx->pinned_groups, group_entry) >> - group_sched_out(event, cpuctx, ctx); >> + perf_event_groups_iterate(&ctx->pinned_groups, >> + group_sched_out_callback, ¶ms); > > So here I would expect to not iterate events where event->cpu != > smp_processor_id() (and ideally not where event->pmu != ctx->pmu). > We still need to iterate thru all groups on thread context switch in and out as well as iterate thru cpu == -1 list (software events) additionally to smp_processor_id() list from multiplexing timer interrupt handler. >> } >> >> if (is_active & EVENT_FLEXIBLE) { >> - list_for_each_entry(event, &ctx->flexible_groups, group_entry) >> - group_sched_out(event, cpuctx, ctx); >> + perf_event_groups_iterate(&ctx->flexible_groups, >> + group_sched_out_callback, ¶ms); > > Idem. > >> } >> perf_pmu_enable(ctx->pmu); >> } > > > I think the rest of the patch is just plumbing to make the above useful. > Let me know if I missed something of value. >