From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: George Spelvin <lkml@SDF.ORG>, Takashi Iwai <tiwai@suse.de>
Cc: linux-kernel@vger.kernel.org, Hannes Reinecke <hare@suse.de>,
linux-scsi@vger.kernel.org,
Marek Lindner <mareklindner@neomailbox.ch>,
Simon Wunderlich <sw@simonwunderlich.de>,
Antonio Quartulli <a@unstable.cc>,
Sven Eckelmann <sven@narfation.org>,
b.a.t.m.a.n@diktynna.open-mesh.org,
Johannes Berg <johannes@sipsolutions.net>,
linux-wireless@vger.kernel.org, Jaroslav Kysela <perex@perex.cz>,
Takashi Iwai <tiwai@suse.com>,
alsa-devel@alsa-project.org
Subject: Re: [RFC PATCH v1 13/50] Avoid some useless msecs/jiffies conversions
Date: Sun, 29 Mar 2020 11:16:47 -0700 [thread overview]
Message-ID: <1585505807.4510.1.camel@HansenPartnership.com> (raw)
In-Reply-To: <20200329175032.GE4675@SDF.ORG>
On Sun, 2020-03-29 at 17:50 +0000, George Spelvin wrote:
> On Sun, Mar 29, 2020 at 07:13:33PM +0200, Takashi Iwai wrote:
> > 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:
> > > > 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...
>
> I'm sorry, I don't understand what you mean by "good at all" here.
> The value computed is exactly the same.
I think he means what the compiler does with it.
We all assume that msecs_to_jiffies is properly optimized so there
should be no need to open code it like you're proposing. So firstly
can you produce the assembly that shows the worse output from
msecs_to_jiffies? If there is a problem, then we should be fixing it
in msecs_to_jiffies, not adding open coding.
James
next prev parent reply other threads:[~2020-03-29 18:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 0:25 [RFC PATCH v1 13/50] Avoid some useless msecs/jiffies conversions George Spelvin
2020-03-29 7:52 ` Takashi Iwai
2020-03-29 12:11 ` George Spelvin
2020-03-29 17:13 ` Takashi Iwai
2020-03-29 17:50 ` George Spelvin
2020-03-29 18:16 ` James Bottomley [this message]
2020-03-29 21:18 ` George Spelvin
2020-03-30 6:27 ` Takashi Iwai
2020-03-30 6:51 ` George Spelvin
2020-03-30 7:29 ` Takashi Iwai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1585505807.4510.1.camel@HansenPartnership.com \
--to=james.bottomley@hansenpartnership.com \
--cc=a@unstable.cc \
--cc=alsa-devel@alsa-project.org \
--cc=b.a.t.m.a.n@diktynna.open-mesh.org \
--cc=hare@suse.de \
--cc=johannes@sipsolutions.net \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=linux-wireless@vger.kernel.org \
--cc=lkml@SDF.ORG \
--cc=mareklindner@neomailbox.ch \
--cc=perex@perex.cz \
--cc=sven@narfation.org \
--cc=sw@simonwunderlich.de \
--cc=tiwai@suse.com \
--cc=tiwai@suse.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox