* Ken Chen ([EMAIL PROTECTED]) wrote: > On 10/18/07, Mathieu Desnoyers <[EMAIL PROTECTED]> wrote: > > Good question indeed. How large is this memory footprint exactly ? If it > > is as small as you say, I suspect that the real issue could be that > > these variable are accessed by the scheduler critical paths and > > therefore trash the caches. > > Maybe my wording was ambiguous, I meant to reduce cache line pollution > when accessing these schedstat fields. > > With unsigned long, on x86_64, schedstat consumes 288 bytes for each > sched_domain and 128 bytes in struct rq. On a extremely small system > that has a couple of CPU sockets with one level of numa node, there > will be 704 bytes per CPU for schedstat. Given the sparseness of > them, we are probably talking about 11-12 cache line eviction on > several heavily used scheduler functions. Reduce cache line pollution > is the primary goal, actual memory consumption isn't really a concern. >
Generally speaking, if such cache trashing is an issue, why don't we make sure that each task struct member is declared in this structure following its access frequency ? (except for #ifdef blocks, which should stay together) It could then statistically save a lot of cachelines. Or is it already the case ? It doesn't look like it when I see: struct list_head ptrace_list; Just beside the struct mm_struct *mm, *active_mm; pointers. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/