On Wed, Jul 18, 2018 at 02:03:18PM +0200, Peter Zijlstra wrote:

Leaving us just 5 bytes short of needing a single cacheline :/

struct ponies {
        unsigned int               tasks[3];                                             /*     0    12 */
        unsigned int               cpu_state:2;                                          /*    12:30  4 */
        unsigned int               io_state:2;                                           /*    12:28  4 */
        unsigned int               mem_state:2;                                          /*    12:26  4 */

        /* XXX 26 bits hole, try to pack */

        /* typedef u64 */ long long unsigned int     last_time;                          /*    16     8 */
        /* typedef u64 */ long long unsigned int     some_time[3];                       /*    24    24 */
        /* typedef u64 */ long long unsigned int     full_time[2];                       /*    48    16 */
        /* --- cacheline 1 boundary (64 bytes) --- */
        /* typedef u64 */ long long unsigned int     nonidle_time;                       /*    64     8 */

        /* size: 72, cachelines: 2, members: 8 */
        /* bit holes: 1, sum bit holes: 26 bits */
        /* last cacheline: 8 bytes */
};

ARGGH!

It _might_ be possible to use curr->se.exec_start for last_time if you
very carefully audit and place the hooks. I've not gone through it in
detail, but it might just work.