LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, frederic@kernel.org,
	cmetcalf@mellanox.com, cl@linux.com, lcapitulino@redhat.com,
	efault@gmx.de, riel@redhat.com, tglx@linutronix.de,
	kernellwp@gmail.com, mingo@kernel.org
Subject: Re: NO_HZ_FULL and tick running within a reasonable amount of time
Date: Tue, 3 Apr 2018 11:23:28 +0200	[thread overview]
Message-ID: <20180403092328.GA4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180402220438.GA15885@linux.vnet.ibm.com>

On Mon, Apr 02, 2018 at 03:04:38PM -0700, Paul E. McKenney wrote:

> The WARN_ON_ONCE() triggering is this guy:
> 
> 	delta = rq_clock_task(rq) - curr->se.exec_start;
> 	WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
> 
> But given that ->se.exec_start is zeroed from time to time, for example,
> in migrate_task_rq_fair(), I am a bit suspicious of this check.
> 
> What am I missing here?

We clear it on migration, but set it when we schedule a task back in.
The above checks that the 'current' task of that CPU had a tick at least
3 seconds ago (to ensure tasks don't go too long without ticks).

The 'current' task is obviously scheduled in and thus must have !0
exec_start time.

  reply	other threads:[~2018-04-03  9:23 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-02 22:04 Paul E. McKenney
2018-04-03  9:23 ` Peter Zijlstra [this message]
2018-04-03 11:41 ` Frederic Weisbecker
2018-04-03 17:08   ` Paul E. McKenney
2018-04-07 13:52     ` Frederic Weisbecker
2018-04-23 13:04     ` Frederic Weisbecker
2018-04-23 13:26       ` Paul E. McKenney
2018-04-14  4:07 Jacek Tomaka

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180403092328.GA4082@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=cl@linux.com \
    --cc=cmetcalf@mellanox.com \
    --cc=efault@gmx.de \
    --cc=frederic@kernel.org \
    --cc=kernellwp@gmail.com \
    --cc=lcapitulino@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=riel@redhat.com \
    --cc=tglx@linutronix.de \
    --subject='Re: NO_HZ_FULL and tick running within a reasonable amount of time' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).