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SubjectRe: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO
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.

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