From: Sultan Alsawaf <sultan@kerneltoast.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
linux-kernel@vger.kernel.org,
"Thomas Gleixner" <tglx@linutronix.de>,
"Peter Zijlstra" <peterz@infradead.org>,
"Theodore Ts'o" <tytso@mit.edu>,
"Jonathan Neuschäfer" <j.neuschaefer@gmx.net>
Subject: Re: [PATCH RFC v1] random: do not take spinlocks in irq handler
Date: Fri, 4 Feb 2022 20:02:26 -0800 [thread overview]
Message-ID: <Yf320i+tVl6MXnD7@sultan-box.localdomain> (raw)
In-Reply-To: <Yf2Q25T04cAxJY3H@linutronix.de>
On Fri, Feb 04, 2022 at 09:47:23PM +0100, Sebastian Andrzej Siewior wrote:
> No need for atomic. If this is truly per-CPU then there will be no
> cross-CPU access, right?
> Therefore I would suggest to use __this_cpu_inc_return() which would avoid
> the sync prefix for the inc operation. Same for __this_cpu_or(). And you
> could use unsigned int.
Hi,
The __this_cpu_{ATOMIC_OP}() functions are for atomically performing a single
per-CPU operation for the current CPU from contexts that permit CPU migration.
Since this code is safe from CPU migrations (add_interrupt_randomness() runs in
hardirq context), the atomic per-CPU helpers are unneeded. Instead of using
__this_cpu_inc_return() and __this_cpu_or(), we can operate on the per-CPU
pointer directly without any extra safety (e.g., `++fast_pool->count` can be
used in place of `__this_cpu_inc_return(irq_randomness.count)`).
Sultan
next prev parent reply other threads:[~2022-02-05 4:02 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-07 12:17 [PATCH 0/5] random: Add PREEMPT_RT support Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 1/5] random: Remove unused irq_flags argument from add_interrupt_randomness() Sebastian Andrzej Siewior
2021-12-07 12:44 ` Wei Liu
2021-12-07 17:35 ` Jason A. Donenfeld
2021-12-07 12:17 ` [PATCH 2/5] irq: Remove unsued flags argument from __handle_irq_event_percpu() Sebastian Andrzej Siewior
2021-12-07 17:41 ` Jason A. Donenfeld
2021-12-11 22:39 ` Thomas Gleixner
2021-12-12 21:13 ` Jason A. Donenfeld
2021-12-07 12:17 ` [PATCH 3/5] random: Split add_interrupt_randomness() Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 4/5] random: Move the fast_pool reset into the caller Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 5/5] random: Defer processing of randomness on PREEMPT_RT Sebastian Andrzej Siewior
2021-12-07 18:14 ` Jason A. Donenfeld
2021-12-07 20:10 ` Sebastian Andrzej Siewior
2021-12-13 15:16 ` Sebastian Andrzej Siewior
2021-12-17 2:23 ` Herbert Xu
2021-12-17 9:00 ` Sebastian Andrzej Siewior
2021-12-18 3:24 ` Herbert Xu
2021-12-19 9:48 ` Sebastian Andrzej Siewior
2021-12-20 2:56 ` Herbert Xu
2021-12-20 14:38 ` Jason A. Donenfeld
2022-01-12 17:49 ` Sebastian Andrzej Siewior
2022-01-30 22:55 ` Jason A. Donenfeld
2022-01-31 16:33 ` Sebastian Andrzej Siewior
2022-02-04 15:31 ` [PATCH RFC v1] random: do not take spinlocks in irq handler Jason A. Donenfeld
2022-02-04 15:58 ` Jason A. Donenfeld
2022-02-04 20:53 ` Sebastian Andrzej Siewior
2022-02-04 20:47 ` Sebastian Andrzej Siewior
2022-02-04 22:08 ` Jason A. Donenfeld
2022-02-04 23:09 ` [PATCH v2] random: defer fast pool mixing to worker Jason A. Donenfeld
2022-02-05 4:02 ` Sultan Alsawaf [this message]
2022-02-05 12:50 ` [PATCH RFC v1] random: do not take spinlocks in irq handler Jason A. Donenfeld
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