On Fri, Dec 15, 2017 at 12:03:31PM +0000, Patrick Bellasi wrote:
> So, by moving util_est right after sched_avg, here is what we get (with some
> lines to better highlight 64B boundaries):
>
> const struct sched_class * sched_class;
> /* 152 8 */
> struct sched_entity {
> [...]
> ---[ Line 9
> ]-------------------------------------------------------------------------------
> struct sched_avg {
> /* typedef u64 */ long long unsigned int
> last_update_time; /* 576 8 */
> /* typedef u64 */ long long unsigned int
> load_sum; /* 584 8 */
> /* typedef u64 */ long long unsigned int
> runnable_load_sum; /* 592 8 */
> /* typedef u32 */ unsigned int util_sum;
> /* 600 4 */
> /* typedef u32 */ unsigned int
> period_contrib; /* 604 4 */
> long unsigned int load_avg;
> /* 608 8 */
> long unsigned int runnable_load_avg;
> /* 616 8 */
> long unsigned int util_avg;
> /* 624 8 */
> } avg; /* 576 56 */
> /* --- cacheline 6 boundary (384 bytes) was 24 bytes
> ago --- */
> struct util_est {
> long unsigned int last;
> /* 632 8 */
> ---[ Line 10
> ]------------------------------------------------------------------------------
> long unsigned int ewma;
> /* 640 8 */
> } util_est; /* 632 16 */
> } se; /* 192 512 */
> ---[ Line 11
> ]------------------------------------------------------------------------------
> /* --- cacheline 9 boundary (576 bytes) was 24 bytes ago ---
> */
> struct sched_rt_entity {
> struct list_head {
> struct list_head * next;
> /* 704 8 */
> struct list_head * prev;
> /* 712 8 */
> } run_list; /* 704 16 */
>
>
> As you can see we still end up with util_est spanning acrosss two cache and
> even worst with an almost empty Line 10. The point is that sched_avg already
> uses 56B... which leave just 8bytes left.
Yes, that's unfortunate.
> So, I can to move util_est there and use unsigned int for "last" and "ewma"
> storage. This should fix the cache alignment but only until we do not add
> other stuff to sched_avg.
>
> BTW, should not be possible to use a similar "fasting" approach for load_avg
> and runnable_load_avg? Given their range a u32 should be just good enough,
> isn't it?
Probably, I'd have to page all that stuff back in :/
Another issue is that for tasks load and runnable_load are the exact
same; I just never found a sensible way to collapse that.
