Re: [RFC PATCH 1/7] cgroup: rstat: only disable interrupts for the percpu lock

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Hello, Hugh.

On Wed, Mar 29, 2023 at 01:38:48PM -0700, Hugh Dickins wrote:
> > So, in general, there's a trade off between local irq service latency and
> > inducing global lock contention when using unprotected locks. With more and
> > more CPUs, the balance keeps shifting. The balance still very much depends
> > on the specifics of a given lock but yeah I think it's something we need to
> > be a lot more careful about now.
> And this looks a very plausible argument to me: I'll let it sink in.

Another somewhat relevant change is that flipping irq on/off used to be
relatively expensive on older x86 cpus. I forget all details about when and
how much but they should be a lot cheaper now. No idea about !x86 cpus tho.

> But I hadn't heard that the RT folks were clamouring for more irq disabling:
> perhaps they partition their machines with more care, and are not devotees
> of high CPU counts.

I think RT folks care a lot more about raw IRQ disables. These shouldn't
actually disable IRQs on RT kernels.



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