netdev - Re: [PATCH v2 00/21] Converge on using secs_to

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Message-ID: <95a461ca-3ed6-4380-ad1a-da12e1109675@csgroup.eu>
Date: Mon, 9 Dec 2024 13:45:17 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Easwar Hariharan <eahariha@...ux.microsoft.com>
Cc: netfilter-devel@...r.kernel.org, coreteam@...filter.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, cocci@...ia.fr,
 linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
 linux-scsi@...r.kernel.org, xen-devel@...ts.xenproject.org,
 linux-block@...r.kernel.org, linux-wireless@...r.kernel.org,
 ath11k@...ts.infradead.org, linux-mm@...ck.org,
 linux-bluetooth@...r.kernel.org, linux-staging@...ts.linux.dev,
 linux-rpi-kernel@...ts.infradead.org, ceph-devel@...r.kernel.org,
 live-patching@...r.kernel.org, linux-sound@...r.kernel.org,
 etnaviv@...ts.freedesktop.org, oss-drivers@...igine.com,
 linuxppc-dev@...ts.ozlabs.org, Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [PATCH v2 00/21] Converge on using secs_to_jiffies()



Le 09/12/2024 à 13:01, Przemek Kitszel a écrit :
> On 12/6/24 9:58 PM, Easwar Hariharan wrote:
>> On 11/29/2024 4:57 AM, Przemek Kitszel wrote:
>>>
>>> [removed most non-list recipients, it's just too much]
>>>
>>> On 11/15/24 10:26 PM, Easwar Hariharan wrote:
>> <snip>
> 
>>>
>>> Regarding code - you could also convert msecs_to_jiffies(const * HZ),
>>> there are 10 that are greppable.
>>>
>>
>> Those seem to be mistakes. const*HZ is a seconds-denominated timeout,
>> being passed to msecs_to_jiffies() which will treat it as a
>> millisecond-denominated timeout resulting in an excessively long
>> timeout. I suppose that's better than a too-short timeout, and
>> apparently it's been working fine all along since hardware responds
>> before the too-long timeout expires. Half of them are in
>> drivers/scsi/arcmsr/arcmsr_hba.c and the pattern has apparently been
>> there since 2010.
> 
> my point was that, the default value of HZ is 1000, and most of the code
> that is just `$value*HZ` was meant as "$value seconds, in ms unit".

I can't follow you here. The default value of HZ is 250 as far as I can see.

Regardless, HZ is the number of jiffies per second, nothing else.

> 
> Same for HZ/const, HZ/2 being 500ms.
> 
> HZ is awful in that it is not 1s but 1/s, but it was easy to abuse the
> value in simple context.

Why is that awful ?

HZ is a nice macro that gives you the number of ticks per second, so 
that you are able to easily calculate the number of ticks for a given 
duration, regardless of the configured number of ticks per second.

Christophe