On 07/22, Peter Zijlstra wrote: > > On Fri, Jul 19, 2019 at 04:37:42PM +0200, Oleg Nesterov wrote: > > On 07/19, Peter Zijlstra wrote: > > > > But I'm still confused, since in the long run, it should still end up > > > with a proportionally divided user/system, irrespective of some short > > > term wobblies. > > > > Why? > > > > Yes, statistically the numbers are proportionally divided. > > This; due to the loss in precision the distribution is like a step > function around the actual s:u ratio line, but on average it still is > s:u.
You know, I am no longer sure... perhaps it is even worse, I need to recheck. > Even if it were a perfect function, we'd still see increments in stime even > if the current program state never does syscalls, simply because it > needs to stay on that s:u line. > > > but you will (probably) never see the real stime == 1000 && utime == 10000 > > numbers if you watch incrementally. > > See, there are no 'real' stime and utime numbers. What we have are user > and system samples -- tick based. Yes, yes, I know. > Sure, we take a shortcut, it wobbles a bit, but seriously, the samples > are inaccurate anyway, so who bloody cares :-) ... > People always complain, just tell em to go pound sand :-) I tried ;) this was my initial reaction to this bug report. However, > You can construct a program that runs 99% in userspace but has all > system samples. Yes, but with the current implementation you do not need to construct such a program, this is what you can easily get "in practice". And this confuses people. They can watch /proc/pid/stat incrementally and (when the numbers are big) find that a program that runs 100% in userspace somehow spends 10 minutes almost entirely in kernel. Or at least more in kernel than in userspace. Even if task->stime doesn't grow at all. Oleg.
