linux-kernel - Re: [PATCH v6] random: clear fast pool, crng, and batches in cpuhp bring up

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Message-ID: <Yg6fbwtNghu76z2V@linutronix.de>
Date:   Thu, 17 Feb 2022 20:18:07 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Theodore Ts'o <tytso@....edu>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v6] random: clear fast pool, crng, and batches in cpuhp
 bring up

On 2022-02-17 19:04:09 [+0100], Jason A. Donenfeld wrote:
> For the irq randomness fast pool, rather than having to use expensive
> atomics, which were visibly the most expensive thing in the entire irq
> handler, simply take care of the extreme edge case of resetting count to
> zero in the cpuhp online handler, just after workqueues have been
> reenabled. This simplifies the code a bit and lets us use vanilla
> variables rather than atomics, and performance should be improved.
> 
> As well, very early on when the CPU comes up, while interrupts are still
> disabled, we clear out the per-cpu crng and its batches, so that it
> always starts with fresh randomness.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Theodore Ts'o <tytso@....edu>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Sultan Alsawaf <sultan@...neltoast.com>
> Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> v6 improves the comments around each of the cpuhp functions, as
> requested.

Perfect thank you.
Did you miss my question regarding cross-CPU init in
random_prepare_cpu()?

Sebastian