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Date: Thu, 2 May 2019 17:06:22 -0700 From: Tim Chen <tim.c.chen@...ux.intel.com> To: Aaron Lu <aaron.lu@...ux.alibaba.com>, Vineeth Remanan Pillai <vpillai@...italocean.com> Cc: Nishanth Aravamudan <naravamudan@...italocean.com>, Julien Desfossez <jdesfossez@...italocean.com>, Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com, fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com, Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.com>, Valentin Schneider <valentin.schneider@....com>, Mel Gorman <mgorman@...hsingularity.net>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Paolo Bonzini <pbonzini@...hat.com> Subject: Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks On 5/1/19 4:27 PM, Tim Chen wrote: > On 4/28/19 11:15 PM, Aaron Lu wrote: >> On Tue, Apr 23, 2019 at 04:18:16PM +0000, Vineeth Remanan Pillai wrote: >>> +/* >>> + * Find left-most (aka, highest priority) task matching @cookie. >>> + */ >>> +struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie) >>> +{ >>> + struct rb_node *node = rq->core_tree.rb_node; >>> + struct task_struct *node_task, *match; >>> + >>> + /* >>> + * The idle task always matches any cookie! >>> + */ >>> + match = idle_sched_class.pick_task(rq); >>> + >>> + while (node) { >>> + node_task = container_of(node, struct task_struct, core_node); >>> + >>> + if (node_task->core_cookie < cookie) { >>> + node = node->rb_left; >> >> Should go right here? >> > > I think Aaron is correct. We order the rb tree where tasks with smaller core cookies > go to the left part of the tree. > > In this case, the cookie we are looking for is larger than the current node's cookie. > It seems like we should move to the right to look for a node with matching cookie. > > At least making the following change still allow us to run the system stably for sysbench. > Need to gather more data to see how performance changes. Pawan ran an experiment setting up 2 VMs, with one VM doing a parallel kernel build and one VM doing sysbench, limiting both VMs to run on 16 cpu threads (8 physical cores), with 8 vcpu for each VM. Making the fix did improve kernel build time by 7%. Tim > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 25638a47c408..ed4cfa49e3f2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -208,9 +208,9 @@ static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie) > while (node) { > node_task = container_of(node, struct task_struct, core_node); > > - if (node_task->core_cookie < cookie) { > + if (cookie < node_task->core_cookie) { > node = node->rb_left; > - } else if (node_task->core_cookie > cookie) { > + } else if (cookie > node_task->core_cookie) { > node = node->rb_right; > } else { > match = node_task; > >
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