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From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 21 Jul 2017 17:09:11 +0200
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Subject: Re: [RFC PATCH v12 3/4] Linux Random Number Generator
To: =?UTF-8?Q?Stephan_M=C3=BCller?= <smueller@chronox.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
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On Fri, Jul 21, 2017 at 10:57 AM, Stephan Müller <smueller@chronox.de> wrote:
> Am Freitag, 21. Juli 2017, 05:08:47 CEST schrieb Theodore Ts'o:

>> Um, the timer is the largest number of interrupts on my system.  Compare:
>>
>>             CPU0       CPU1       CPU2       CPU3
>>  LOC:    6396552    6038865    6558646    6057102   Local timer interrupts
>>
>> with the number of disk related interrupts:
>>
>>  120:      21492     139284      40513    1705886   PCI-MSI 376832-edge
>> ahci[0000:00:17.0]
>
> They seem to be not picked up with the add_interrupt_randomness function.

On x86, the local APIC timer has some special handling in
arch/x86/entry/entry_64.S that does not go through handle_irq_event().

I would assume that this is different when you boot with the "noapictimer"
option and use the hpet clockevent instead.

On other architectures, the timer interrupt is often handled as a regular
IRQ as well.

       Arnd