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Date: Thu, 06 Mar 2014 14:36:17 -0500 From: Rik van Riel <riel@...hat.com> To: Frederic Weisbecker <fweisbec@...il.com>, LKML <linux-kernel@...r.kernel.org> CC: Ingo Molnar <mingo@...nel.org>, Marcelo Tosatti <mtosatti@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de> 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 <huding@...hat.com> > Reported-by: Marcelo Tosatti <mtosatti@...hat.com> > Cc: Ingo Molnar <mingo@...nel.org> > Cc: Marcelo Tosatti <mtosatti@...hat.com> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Thomas Gleixner <tglx@...utronix.de> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> Acked-by: Rik van Riel <riel@...hat.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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