linux-kernel - Re: [RFC PATCH v1 13/50] Avoid some useless msecs/jiffies conversions

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Date:   Sun, 29 Mar 2020 19:13:33 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     George Spelvin <lkml@....ORG>
Cc:     linux-kernel@...r.kernel.org, Hannes Reinecke <hare@...e.de>,
        linux-scsi@...r.kernel.org,
        Marek Lindner <mareklindner@...mailbox.ch>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Antonio Quartulli <a@...table.cc>,
        Sven Eckelmann <sven@...fation.org>,
        b.a.t.m.a.n@...tynna.open-mesh.org,
        Johannes Berg <johannes@...solutions.net>,
        linux-wireless@...r.kernel.org, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        lkml@....org
Subject: Re: [RFC PATCH v1 13/50] Avoid some useless msecs/jiffies conversions

On Sun, 29 Mar 2020 14:11:29 +0200,
George Spelvin wrote:
> 
> On Sun, Mar 29, 2020 at 09:52:23AM +0200, Takashi Iwai wrote:
> > On Thu, 22 Aug 2019 02:25:10 +0200, George Spelvin wrote:
> >> Likewise, "msecs_to_jiffies(seconds * 1000)" is more
> >> conveniently written "seconds * HZ".
> > 
> > I thought the compiler already optimizes to the constant calculation
> > for the above case?
> 
> It optimizes that if the entire argument, including "seconds", is
> a compile-time constant.
> 
> However, given "msecs_to_jiffies(hdev->rpa_timeout * 1000);",
> the computatin is non-trivial.

Fair enough.  But it's still a question whether an open code X * HZ is
good at all...


thanks,

Takashi