Yuyang Du <yuyang...@intel.com> writes: > On Mon, Sep 14, 2015 at 10:34:00AM -0700, bseg...@google.com wrote: >> >> SCHED_LOAD_RESOLUTION and the non-SLR part of SCHED_LOAD_SHIFT are not >> >> required to be the same value and should not be conflated. >> >> >> >> In particular, since cgroups are on the same timeline as tasks and their >> >> shares are not scaled by SCHED_LOAD_SHIFT in any way (but are scaled so >> >> that SCHED_LOAD_RESOLUTION is invisible), changing that part of >> >> SCHED_LOAD_SHIFT would cause issues, since things can assume that nice-0 >> >> = 1024. However changing SCHED_LOAD_RESOLUTION would be fine, as that is >> >> an internal value to the kernel. >> >> >> >> In addition, changing the non-SLR part of SCHED_LOAD_SHIFT would require >> >> recomputing all of prio_to_weight/wmult for the new NICE_0_LOAD. >> > >> > I think I follow, but doesn't that mean that the current code is broken >> > too? NICE_0_LOAD changes if you change SCHED_LOAD_RESOLUTION: >> > >> > #define SCHED_LOAD_SHIFT (10 + SCHED_LOAD_RESOLUTION) >> > #define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT) >> > >> > #define NICE_0_LOAD SCHED_LOAD_SCALE >> > #define NICE_0_SHIFT SCHED_LOAD_SHIFT >> > >> > To me it sounds like we need to define it the other way around: >> > >> > #define NICE_0_SHIFT 10 >> > #define NICE_0_LOAD (1L << NICE_0_SHIFT) >> > >> > and then add any additional resolution bits from there to ensure that >> > NICE_0_LOAD and the prio_to_weight/wmult tables are unchanged. >> >> No, NICE_0_LOAD is supposed to be scale_load(prio_to_weight[nice_0]), >> ie including SLR. It has never been clear to me what >> SCHED_LOAD_SCALE/SCHED_LOAD_SHIFT were for as opposed to NICE_0_LOAD, >> and the new utilization uses of it are entirely unlinked to 1024 == NICE_0 > > Presume your SLR means SCHED_LOAD_RESOLUTION: > > 1) The introduction of (not redefinition of) SCHED_RESOLUTION_SHIFT does not > change anything after macro expansion. > > 2) The constants in prio_to_weight[] and prio_to_wmult[] are tied to a > resolution of 10bits NICE_0, i.e., 1024, I guest it is the user visible > part you mentioned, so is the cgroup share. > > To me, it is all ok. With the SCHED_RESOLUTION_SHIFT, the basic resolution > unit, it is just for us to state clearly, the NICE_0's weight has a fixed > resolution of SCHED_RESOLUTION_SHIFT, or even add this: > > #if prio_to_weight[20] != 1 << SCHED_RESOLUTION_SHIFT > error "NICE_0 weight not calibrated" > #endif > /* I can learn, Peter */ > > I guess you are saying we are conflating NICE_0 with NICE_0_LOAD. But to me, > they are just integer metrics, needing a resolution respectively. That is it.
Yes this would change nothing at the moment post-expansion, that's not the point. SLR being 10 bits and the nice-0 being 1024 are completely and utterly unrelated and the headers should not pretend they need to be the same value, any more than there should be a #define that is shared with every other use of 1024 in the kernel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
