Re: [PATCH v2 00/21] Converge on using secs_to_jiffies()

[Christophe Leroy <christophe.leroy@xxxxxxxxxx>]

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