Messages in this thread | | | Date | Thu, 11 Apr 2013 17:17:15 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH -tip 0/4] do not make cputime scaling in kernel |
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On Mon, Apr 08, 2013 at 05:32:50PM +0200, Ingo Molnar wrote: > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > 2013/4/4 Stanislaw Gruszka <sgruszka@redhat.com>: > > > On Thu, Apr 04, 2013 at 02:31:42PM +0200, Frederic Weisbecker wrote: > > >> I don't know. I'm not convinced userland is the right place to perform > > >> this kind of check. The kernel perhaps doesn't give guarantee about > > >> utime/stime precision but now users may have got used to that scaled > > >> behaviour. It's also a matter of security, a malicous app can hide > > >> from the tick to make its activity less visible from tools like top. > > >> > > >> It's sortof an ABI breakage to remove such an implicit protection. And > > >> fixing that from userspace with a lib or so won't change that fact. > > > > > > I think number of fields in /proc/PID/stat is not part of ABI. For > > > example commit 5b172087f99189416d5f47fd7ab5e6fb762a9ba3 add various > > > new fields at the end of the file. What is imported to keep unchanged > > > ABI is not changing order or meaning of fields we already have. > > > > Oh I wasn't considering the layout of the proc file but the semantic > > change in its utime/stime fields. > > Btw., even the ordering of fields in /proc/PID/stat might be an ABI, iif an > application relies on it and breaks if we change it.
Sure, but it seems there are exceptions as in the above mentioned commit.
> > What matters is what applications do, not what we think they do or what we think > they should do in an ideal world.
Agreed.
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