Re: [PATCH 2/7] aio-posix: move RCU_READ_LOCK() into run_poll_handlers()

[Paolo Bonzini]

On 05/03/20 18:08, Stefan Hajnoczi wrote:
>  
> +    /*
> +     * Optimization: ->io_poll() handlers often contain RCU read critical
> +     * sections and we therefore see many rcu_read_lock() -> 
> rcu_read_unlock()
> +     * -> rcu_read_lock() -> ... sequences with expensive memory
> +     * synchronization primitives.  Make the entire polling loop an RCU
> +     * critical section because nested rcu_read_lock()/rcu_read_unlock() 
> calls
> +     * are cheap.
> +     */
> +    RCU_READ_LOCK_GUARD();
> +

Looks good, but I suggest that you compile with --enable-membarrier as
that makes RCU critical sections basically free.

Paolo