On Mon, Jan 30, 2017 at 03:32:24PM +0100, Stanislaw Gruszka wrote: > On Mon, Jan 30, 2017 at 05:46:43AM +0100, Frederic Weisbecker wrote: > > Now lets admit one drawback: s390 and powerpc with > > CONFIG_VIRT_CPU_ACCOUNTING_NATIVE have new cputime_t to nsecs conversion > > on cputime accounting path. But this should be leveraged by the recent > > changes which delay the cputime accounting to tick and context switch. > > I think it would be worth to mention that there are other drawbacks on > 32bit architectures that use cputime-jiffies currently, like: > - cache utilization will be worse
Due to utime and stime becoming 64 bits? Yeah indeed. > - conversion cputime_to_jiffies() and cputime_to_clock_t() (with HZ == > USER_HS) > will no longer be an no-op Yes probably some cputime_to_jiffies() have been replaced with nsecs_to_jiffies(). In turn many cputime_to_nsecs() are now no-op. Now concerning cputime_to_clock_t(), it seems that USER_HZ=100 most of the time. This value seems to be seldom used for HZ on distros in general. > - to keep values consistent will need to add protection of u64 store/load, > which will create additional performance costs Yes but note these issues were already there before this patchset. Especially for kcpustat. And utime/stime also have these issues under CONFIG_NO_HZ_FULL. Now this patchset extends the problem for utime/stime to all configs. That's certainly one more reason to fix it. But that's outside the scope of this patchset.
