Re: [PATCH v2] blk-cgroup: Replace u64_sync with blkg_stat_lock for stats update

[tj@xxxxxxxxxx]

Hello,

On Thu, Jul 11, 2024 at 02:25:29AM +0000, Boy Wu (吳勃誼) wrote:
...
> I can remove the 32bit only define, but I think we need to add back the
> u64 sync, because the spin lock and the u64 sync serve different
> purposes. The spin lock is for handling concurrent problems from
> different CPUs updating stats, and u64 sync is for updating 64 bits
> data and fetching 64 bits data from different CPUs in 32bit SMP
> systems.

Hmm... so what I'm suggesting is using u64_sync for the per-cpu stat
structure as they are guaranteed to have only one updater with irq disabled
and use a spinlock for the shared iostat which can have multiple updaters
and isn't accessed that frequently.

Thanks.

-- 
tejun