Messages in this thread | | | Date | Sat, 5 Mar 2016 11:27:01 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] steal_account_process_tick() should return jiffies |
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Chris,
On Fri, 4 Mar 2016, Chris Friesen wrote:
First of all the subject line should contain a subsystem prefix, i.e. "sched/cputime:"
> The callers of steal_account_process_tick() expect it to return whether > the last jiffy was stolen or not. > > Currently the return value of steal_account_process_tick() is in units > of cputime, which vary between either jiffies or nsecs depending on > CONFIG_VIRT_CPU_ACCOUNTING_GEN.
Sure, but what is the actual problem? The return value is boolean and tells whether there was stolen time accounted or not.
> The fix is to change steal_account_process_tick() to always return > jiffies. If CONFIG_VIRT_CPU_ACCOUNTING_GEN is not enabled then this > is a no-op.
What does that fix?
> As far as I can tell this bug has been present since commit dee08a72.
Which bug?
> Signed-off-by: Chris Friesen <chris.friesen@windriver.com> > --- > > kernel/sched/cputime.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index b2ab2ff..e724496 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -276,7 +276,7 @@ static __always_inline bool steal_account_process_tick(void) > this_rq()->prev_steal_time += cputime_to_nsecs(steal_ct); > > account_steal_time(steal_ct); > - return steal_ct; > + return cputime_to_jiffies(steal_ct);
So if steal time is close to a jiffie, then cputime_to_jiffies will return 0 and you account a full jiffie to user/system/whatever.
Without a proper explanation of the problem and the resulting "bug" I really cannot figure out why we want that change.
Thanks,
tglx
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