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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B064C433EF for ; Tue, 21 Dec 2021 03:00:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234262AbhLUDAq (ORCPT ); Mon, 20 Dec 2021 22:00:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231801AbhLUDAi (ORCPT ); Mon, 20 Dec 2021 22:00:38 -0500 Received: from mail-yb1-xb31.google.com (mail-yb1-xb31.google.com [IPv6:2607:f8b0:4864:20::b31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6C69C061574 for ; Mon, 20 Dec 2021 19:00:37 -0800 (PST) Received: by mail-yb1-xb31.google.com with SMTP id y68so34677434ybe.1 for ; Mon, 20 Dec 2021 19:00:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=w3hfyn0AnggC0kICOCglW5QgoayhFGYuLDjb6KNPNVA=; b=gVZw/IU2GHHe7dotMph1q5tkyUIMWBgPLtT8YGK8ow2eq16cRDQPVLTINJrwMzYmJX SZ5kB3g/NITBdaM1QZJdpitcF7Ao+xvuyQb5ou74nx1sw+XfsS82F+eUAeCgqG3O9TUd oeXoHEuofv4kYYe8e8B8aL2AU3j/tL6Vx+LlJdoV1R01hZ55S61O14PG3OiSR1YMdGXQ bwS+X1atPefvcHRTdMAqwSFAW+5MnO62gN/iSfy9iRh21gTLT+ym9CNJlbyGPVlX74pL 6fbLJmBbykWz6BFFTZnEB7YAlnTK+fL6rS0MFve4lL5l6P+WKvwrU/F7styXhSlzcJBn ofBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=w3hfyn0AnggC0kICOCglW5QgoayhFGYuLDjb6KNPNVA=; b=m4ECIHPrX8rkIYGbeaSocyhE1B9+OKKKsLbk9zMWWmhpB0cKrYajvdsb4IFhi+6NXk qB7y5hxPzrET27oJmsPPmmu0wj+MR/pKpqHjNcD3wMF6KpRCU50rzubtxkxJx372wd8L eBUjoDZqkbuI7xeOSjD1hahNsmscZubW9Xy52Uuo9IS2yDBCemNohLGqmpeqCfdePNvk DRYlk+pSUUXO1qT00b8T3Z+afZbesx7b9jMGyQPkOPe7TJxJz8SDnlt4ciHxHuITgpoO NqHeCFTqaLwYC1M6qJ0pQz+Lzrv1CqB2pbEq5TPqMPTDRufmz82au7tuOe6pjyNDa+3g fX4g== X-Gm-Message-State: AOAM5334/m3rDMxOLSwDHh6rfVFpv99TdPMmPjYVaRrQngWr4Wz4YAe5 BSLIdWHf3JQCFs0U47dqwJLN3XSAwudHyTgntVy92g== X-Google-Smtp-Source: ABdhPJwCOEv8yqzq85M00wMxnRtFfuBwX+8GjWFjy6cT1V42/iAHhfaq6bfddz/ZqAgyKauQ6YDsQEOPO9nuJNCKJzI= X-Received: by 2002:a25:b3cc:: with SMTP id x12mr1827834ybf.243.1640055636690; Mon, 20 Dec 2021 19:00:36 -0800 (PST) MIME-Version: 1.0 References: <1639721264-12294-1-git-send-email-huangzhaoyang@gmail.com> In-Reply-To: From: Suren Baghdasaryan Date: Mon, 20 Dec 2021 19:00:25 -0800 Message-ID: Subject: Re: [PATCH] psi: fix possible trigger missing in the window To: Zhaoyang Huang Cc: Johannes Weiner , Zhaoyang Huang , "open list:MEMORY MANAGEMENT" , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 20, 2021 at 6:51 PM Zhaoyang Huang wrote: > > On Tue, Dec 21, 2021 at 10:30 AM Suren Baghdasaryan wrote: > > > > On Mon, Dec 20, 2021 at 5:57 PM Zhaoyang Huang wrote: > > > > > > On Tue, Dec 21, 2021 at 3:58 AM Suren Baghdasaryan wrote: > > > > > > > > On Fri, Dec 17, 2021 at 10:03 PM Zhaoyang Huang wrote: > > > > > > > > > > loop Suren > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > On Fri, Dec 17, 2021 at 2:08 PM Huangzhaoyang wrote: > > > > > > > > > > > > From: Zhaoyang Huang > > > > > > > > > > > > There could be missing wake up if the rest of the window remain the > > > > > > same stall states as the polling_total updates for every polling_min_period. > > > > > > > > Could you please expand on this description? I'm unclear what the > > > > problem is. I assume "polling_min_period" in this description refers > > > > to the group->poll_min_period. > > > > > > > > From the code, looks like the change results in update_triggers() > > > > calling window_update() once there was a new stall recorded for the > > > > trigger state and until the tracking window is complete. I don't see > > > > the point of calling window_update() if there was no stall change > > > > since the last call to window_update(). The resulting growth will not > > > > increase if there is no new stall. > > > > Maybe what you want to achieve here is more than one trigger per > > > > window if the stall limit was breached? If so, then this goes against > > > > the design for psi triggers in which we want to rate-limit the number > > > > of generated triggers per tracking window (see: > > > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L545). > > > > Please clarify the issue and the intentions here. > > > > Thanks! > > > Please correct me if I am wrong. Imagine that there is a new stall > > > during the 1st polling_min_period among 10 of them in the window and > > > group->polling_total will be updated to total without trigger. If the > > > rest of 9 polling_min_periods remain the same states, the trigger will > > > be missed when window timing is reached. > > > > I don't see why updating group->polling_total after the first > > registered stall is an issue here. window_update() calculates growth > > using current group->total[] and win->start_value (see: > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L483) > > which is set at the beginning of the window (see: > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L462). > > If the calculated growth did not reach t->threshold then the trigger > > should not be fired (see: > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L542). > > We fire the trigger only if growth within a given window is higher > > than the threshold. > > > > In your scenario if the stall recorded in the 1st polling_min_period > > was less than the threshold and in the other 9 polling_min_periods no > > new stalls were registered then there should be no triggers fired in > > that window. This is intended behavior. Trigger is fired only when the > The stall in the 1st polling_min_period was *LARGE* then the threshold > will also be ignored here. Ok, in that case is it ignored due to this condition: https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L546 ? If so then I see what the problem might be. Please confirm. > > > recorded stall within the window breaches the threshold. And there > > will be only one trigger generated per window, no matter how much > > stall is being recorded after the threshold was breached. > > Hopefully this clarifies the behavior? > > I don't think so. According to your opinion, if the total keeps no > change in the last polling_min_period, then the growth during the 1-9 > min_periods which is much larger than the threshold will also be > ignored. It does not make sense. > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L529 > > > > > > > > > > > > > > > > > > Signed-off-by: Zhaoyang Huang > > > > > > --- > > > > > > include/linux/psi_types.h | 2 ++ > > > > > > kernel/sched/psi.c | 30 ++++++++++++++++++------------ > > > > > > 2 files changed, 20 insertions(+), 12 deletions(-) > > > > > > > > > > > > diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h > > > > > > index 0a23300..9533d2e 100644 > > > > > > --- a/include/linux/psi_types.h > > > > > > +++ b/include/linux/psi_types.h > > > > > > @@ -132,6 +132,8 @@ struct psi_trigger { > > > > > > > > > > > > /* Refcounting to prevent premature destruction */ > > > > > > struct kref refcount; > > > > > > + > > > > > > + bool new_stall; > > > > > > }; > > > > > > > > > > > > struct psi_group { > > > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > > > > > index 1652f2b..402718c 100644 > > > > > > --- a/kernel/sched/psi.c > > > > > > +++ b/kernel/sched/psi.c > > > > > > @@ -458,9 +458,12 @@ static void psi_avgs_work(struct work_struct *work) > > > > > > static void window_reset(struct psi_window *win, u64 now, u64 value, > > > > > > u64 prev_growth) > > > > > > { > > > > > > + struct psi_trigger *t = container_of(win, struct psi_trigger, win); > > > > > > + > > > > > > win->start_time = now; > > > > > > win->start_value = value; > > > > > > win->prev_growth = prev_growth; > > > > > > + t->new_stall = false; > > > > > > } > > > > > > > > > > > > /* > > > > > > @@ -515,7 +518,6 @@ static void init_triggers(struct psi_group *group, u64 now) > > > > > > static u64 update_triggers(struct psi_group *group, u64 now) > > > > > > { > > > > > > struct psi_trigger *t; > > > > > > - bool new_stall = false; > > > > > > u64 *total = group->total[PSI_POLL]; > > > > > > > > > > > > /* > > > > > > @@ -523,19 +525,26 @@ static u64 update_triggers(struct psi_group *group, u64 now) > > > > > > * watchers know when their specified thresholds are exceeded. > > > > > > */ > > > > > > list_for_each_entry(t, &group->triggers, node) { > > > > > > - u64 growth; > > > > > > - > > > > > > /* Check for stall activity */ > > > > > > if (group->polling_total[t->state] == total[t->state]) > > > > > > continue; > > > > > > > > > > > > /* > > > > > > - * Multiple triggers might be looking at the same state, > > > > > > - * remember to update group->polling_total[] once we've > > > > > > - * been through all of them. Also remember to extend the > > > > > > - * polling time if we see new stall activity. > > > > > > + * update the trigger if there is new stall which will be > > > > > > + * reset when run out of the window > > > > > > */ > > > > > > - new_stall = true; > > > > > > + t->new_stall = true; > > > > > > + > > > > > > + memcpy(&group->polling_total[t->state], &total[t->state], > > > > > > + sizeof(group->polling_total[t->state])); > > > > > > + } > > > > > > + > > > > > > + list_for_each_entry(t, &group->triggers, node) { > > > > > > + u64 growth; > > > > > > + > > > > > > + /* check if new stall happened during this window*/ > > > > > > + if (!t->new_stall) > > > > > > + continue; > > > > > > > > > > > > /* Calculate growth since last update */ > > > > > > growth = window_update(&t->win, now, total[t->state]); > > > > > > @@ -552,10 +561,6 @@ static u64 update_triggers(struct psi_group *group, u64 now) > > > > > > t->last_event_time = now; > > > > > > } > > > > > > > > > > > > - if (new_stall) > > > > > > - memcpy(group->polling_total, total, > > > > > > - sizeof(group->polling_total)); > > > > > > - > > > > > > return now + group->poll_min_period; > > > > > > } > > > > > > > > > > > > @@ -1152,6 +1157,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, > > > > > > t->last_event_time = 0; > > > > > > init_waitqueue_head(&t->event_wait); > > > > > > kref_init(&t->refcount); > > > > > > + t->new_stall = false; > > > > > > > > > > > > mutex_lock(&group->trigger_lock); > > > > > > > > > > > > -- > > > > > > 1.9.1 > > > > > >