linux-kernel - Re: [PATCH] random: avoid reading two cache lines on irq randomness

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Message-ID: <YzQyEFMNCcDmJMdX@linutronix.de>
Date:   Wed, 28 Sep 2022 13:37:52 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org,
        Sultan Alsawaf <sultan@...neltoast.com>
Subject: Re: [PATCH] random: avoid reading two cache lines on irq randomness

On 2022-09-23 20:28:49 [+0200], Jason A. Donenfeld wrote:
> In order to avoid reading and dirtying two cache lines on every IRQ, move
> the work_struct to the bottom of the fast_pool struct. add_interrupt_
> randomness() always touches .pool and .count, which are currently split,
> because .mix pushes everything down. Instead, move .mix to the bottom,
> so that .pool and .count are always in the first cache line, since the
> .mix is only accessed when the pool is full.
> 
> Fixes: 58340f8e952b ("random: defer fast pool mixing to worker")
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Sultan Alsawaf <sultan@...neltoast.com>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Yup, makes sense.

Sebastian