From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751303AbdBWJuv (ORCPT <rfc822;w@1wt.eu>);
        Thu, 23 Feb 2017 04:50:51 -0500
Received: from bombadil.infradead.org ([65.50.211.133]:38319 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750944AbdBWJuu (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 23 Feb 2017 04:50:50 -0500
Date: Thu, 23 Feb 2017 10:50:50 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Pavan Kondeti <pkondeti@codeaurora.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>
Subject: Re: min_vruntime update when a task is sleeping/migrating
Message-ID: <20170223095050.GA6515@twins.programming.kicks-ass.net>
References: <CAEU1=PnD3KuA-Wau9J7YLsUh_9xO9wFT2DvXSOWJ5HLVtCRHRg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAEU1=PnD3KuA-Wau9J7YLsUh_9xO9wFT2DvXSOWJ5HLVtCRHRg@mail.gmail.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Feb 23, 2017 at 11:45:26AM +0530, Pavan Kondeti wrote:
> Hi Peter,
> 
> The comment and the code around 2nd update_min_vruntime() call in
> dequeue_entity() are not matching. If I understand commit b60205c7c558
> ("sched/fair: Fix min_vruntime tracking") correctly, the check is
> inverted there. We want to update min_vruntime when a task is
> sleeping/migrating. is my understanding right?

Hurm, yes that comment and the code are not in agreement :/

Having gone over the code again, I think the comment is right and the
code is wrong, but it would be good to double check that.

> static void
> dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> {
> 
>  <snip>
>   /*
>    * Now advance min_vruntime if @se was the entity holding it back,
>    * except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case we'll be
>    * put back on, and if we advance min_vruntime, we'll be placed back
>    * further than we started -- ie. we'll be penalized.
>    */
>    if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
>       update_min_vruntime(cfs_rq);
> }