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Date:	Thu, 06 Mar 2014 14:36:17 -0500
From:	Rik van Riel <>
To:	Frederic Weisbecker <>,
	LKML <>
CC:	Ingo Molnar <>,
	Marcelo Tosatti <>,
	Peter Zijlstra <>,
	Thomas Gleixner <>
Subject: Re: [PATCH 4/6] cputime: Fix jiffies based cputime assumption on
 steal accounting

On 03/06/2014 12:56 PM, Frederic Weisbecker wrote:
> The steal guest time accounting code assumes that cputime_t is based on
> jiffies. So when CONFIG_NO_HZ_FULL=y, which implies that cputime_t
> is based on nsecs, steal_account_process_tick() passes the delta in
> jiffies to account_steal_time() which then accounts it as if it's a
> value in nsecs.
> As a result, accounting 1 second of steal time (with HZ=100 that would
> be 100 jiffies) is spuriously accounted as 100 nsecs.
> As such /proc/stat may report 0 values of steal time even when two
> guests have run concurrently for a few seconds on the same host and
> same CPU.
> In order to fix this, lets convert the nsecs based steal delta to
> cputime instead of jiffies by using the right conversion API.
> Given that the steal time is stored in cputime_t and this type can have
> a smaller granularity than nsecs, we only account the rounded converted
> value and leave the remaining nsecs for the next deltas.
> Reported-by: Huiqingding <>
> Reported-by: Marcelo Tosatti <>
> Cc: Ingo Molnar <>
> Cc: Marcelo Tosatti <>
> Cc: Peter Zijlstra <>
> Cc: Thomas Gleixner <>
> Signed-off-by: Frederic Weisbecker <>

Acked-by: Rik van Riel <>

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