From: Peter Zijlstra <peterz@infradead.org>
To: byungchul.park@lge.com
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, efault@gmx.de,
tglx@linutronix.de, yuyang.du@intel.com, pjt@google.com
Subject: Re: [PATCH] sched: prevent getting too much vruntime
Date: Wed, 11 Nov 2015 10:26:32 +0100 [thread overview]
Message-ID: <20151111092632.GK17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1447231827-1891-1-git-send-email-byungchul.park@lge.com>
On Wed, Nov 11, 2015 at 05:50:27PM +0900, byungchul.park@lge.com wrote:
I've not actually read anything; my brain isn't working right today.
> +static inline void vruntime_unnormalize(struct cfs_rq *cfs_rq, struct sched_entity *se)
> +{
> + se->vruntime += cfs_rq->min_vruntime;
> + if (unlikely((s64)se->vruntime < 0))
> + se->vruntime = 0;
> +}
But this is broken. This simply _cannot_ be right.
vruntime very much needs to wrap in u64 space. While regular time in ns
takes some 584 year to wrap, vruntime is scaled. The fastest vruntime is
2/1024 or 512 times faster than normal time. Making it take just over a
year to wrap around. This will happen.
next prev parent reply other threads:[~2015-11-11 9:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-11 8:50 byungchul.park
2015-11-11 9:26 ` Peter Zijlstra [this message]
2015-11-11 9:48 ` Byungchul Park
2015-11-11 11:50 ` Peter Zijlstra
2015-11-12 5:10 ` Byungchul Park
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