Re: [PATCH] sched/fair: provide u64 read for 32-bits arch helper

From: peterz
Date: Mon Jul 27 2020 - 08:38:09 EST

On Mon, Jul 27, 2020 at 11:59:24AM +0100, vincent.donnefort@xxxxxxx wrote:
> From: Vincent Donnefort <vincent.donnefort@xxxxxxx>
> Introducing two macro helpers u64_32read() and u64_32read_set_copy() to
> factorize the u64 vminruntime and last_update_time read on a 32-bits
> architecture. Those new helpers encapsulate smp_rmb() and smp_wmb()
> synchronization and therefore, have a small penalty in set_task_rq_fair()
> and init_cfs_rq().
> The choice of using a macro over an inline function is driven by the
> conditional u64 variable copy declarations.
> #ifndef CONFIG_64BIT
> u64 [vminruntime|last_update_time]_copy;
> #endif

This lacks a *why*... why did you get up this morning and wrote us this