linux-kernel - Re: [PATCH] random: move initialization functions out of hot pages

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Date:   Sun, 15 May 2022 13:13:28 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] random: move initialization functions out of hot pages

Am Fri, May 13, 2022 at 04:29:08PM +0200 schrieb Jason A. Donenfeld:
> Much of random.c is devoted to initializing the rng and accounting for
> when a sufficient amount of entropy has been added. In a perfect world,
> this would all happen during init, and so we could mark these functions
> as __init. But in reality, this isn't the case: sometimes the rng only
> finishes initializing some seconds after system init is finished.
> 
> For this reason, at the moment, a whole host of functions that are only
> used relatively close to system init and then never again are intermixed
> with functions that are used in hot code all the time. This creates more
> cache misses than necessary.
> 
> In order to pack the hot code closer together, this commit moves the
> initialization functions that can't be marked as __init into
> .text.unlikely by way of the __cold attribute.
> 
> Of particular note is moving credit_init_bits() into a macro wrapper
> that inlines the crng_ready() static branch check. This avoids a
> function call to a nop+ret, and most notably prevents extra entropy
> arithmetic from being computed in mix_interrupt_randomness().

	Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>

Thanks,
	Dominik