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

[Linus Torvalds]

On Wed, Jul 18, 2018 at 5:03 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> And as said before, we can compress the state from 12 bytes, to 6 bits
> (or 1 byte), giving another 11 bytes for 59 bytes free.
>
> Leaving us just 5 bytes short of needing a single cacheline :/

Do you actually need 64 bits for the times?

That's the big cost. And it seems ridiculous, if you actually care about size.

You already have a 64-bit start time. Everything else is some
cumulative relative time. Do those really need 64-bit and nanosecond
resolution?

Maybe a 32-bit microsecond would be ok - would you ever account more
than 35 minutes of anything without starting anew?

             Linus