On Tue, Jan 17, 2023 at 10:50:39PM +0100, Thomas Gleixner wrote:

On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:

quoted

The IRQ domain structures are currently protected by the global
irq_domain_mutex. Switch to using more fine-grained per-domain locking,
which may potentially speed up parallel probing somewhat.

Does it or not?

If not then why adding all this churn for no real value?

It probably doesn't make much difference, but Marc wanted per-domain
locking:

    > I'd really like to avoid a global mutex. At the very least this should
    > be a per-domain mutex, otherwise this will serialise a lot more than
    > what is needed.
    
    Yeah, I considered that too, but wanted to get your comments on this
    first.
    
    Also note that the likewise global irq_domain_mutex (and
    sparse_irq_lock) are taken in some of these paths so perhaps using finer
    locking won't actually matter that much as this is mostly for parallel
    probing.

    https://lore.kernel.org/lkml/YuKHiZuNvN+K9NCc@hovoldconsulting.com/ (local)

As part of fixing the races, this series has now replaced the per-domain
revmap mutexes with the global irq_domain_mutex, which could possibly be
perceived as a step in the wrong direction in this respect.

This patch restores per-domain locking for non-hierarchical domains and
extends it to hierarchical domains. This leaves the irq_domain_mutex to
only be used for things that actually need a global lock such as the
domain list.

I consider this mostly a clean up, and I did intentionally place it last
in order to not have the fixes depend on it.

Johan

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