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From: Andrew Morton <akpm@linux-foundation.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Dave Young" <hidave.darkstar@gmail.com>,
	"Johannes Weiner" <hannes@saeurebad.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] add time_now_after and other macros which compare with jiffies
Date: Sun, 9 Mar 2008 11:36:01 -0700	[thread overview]
Message-ID: <20080309113601.b8552a79.akpm@linux-foundation.org> (raw)
In-Reply-To: <20080309095802.70d91c7b@core>

On Sun, 9 Mar 2008 09:58:02 +0000 Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> > >  > +/* time_now_before_eq(a) return true if now (jiffies) is before or equal to a */
> > >  > +#define time_now_before_eq(a) time_before_eq(jiffies, a)
> > >
> > >  How about even more obvious names like time_is_past(), time_is_future(),
> > >  ...?
> > 
> > Thanks for comment.
> > 
> > Then how do we name the _eq version?  IMHO, the time_now_* is enough.
> 
> Why do you even need them. I don't see the point of *any* of these extra
> macros as they simply obfuscate code and hide what is actually going on.

Two reasons:

a) the existing macros are (I believe) a right royal pita.  It's very
   hard to remember which order the args are supposed to be in.

   So each time I see a time_foo() when reviewing a patch I have to go
   off and re-read the implementation then have a big think to check that
   they got it right (a sure sign of a poor interface, no)?

   And I'm not the only one - people get this wrong fairly regularly.

b) around 90% of the usages of time_after() are to compare against jiffies!

The macros which Dave is developing aren't just less-error-prone,
easier-to-review transformations - they offer higher-level functionality.
Because time_after() is just a basic comparison operation, whereas
time_now_before() is an *application* of that operation.

Trust me on this - they will lead to easier-to-review code and less bugs.

> The initial macros were added because of the type safety and correct
> comparison rules being complex. They have a purpose.

They are hard to use and hard to review.

> Even if you want these you can use !time_future() if you don't want the
> _eq variants. Generally speaking drivers should be using timers not
> polled loops, and most of our loops comparing with jiffies want removing.


  parent reply	other threads:[~2008-03-09 18:36 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-07 23:35 Dave Young
2008-03-08 16:12 ` Johannes Weiner
2008-03-09  0:54   ` Dave Young
2008-03-09  9:58     ` Alan Cox
2008-03-09 10:44       ` Dave Young
2008-03-09 11:08         ` Alan Cox
2008-03-09 19:01           ` Andrew Morton
2008-03-09 20:06             ` Alan Cox
2008-03-10  2:03             ` Dave Young
2008-03-10  2:41               ` Johannes Weiner
2008-03-09 18:36       ` Andrew Morton [this message]
2008-03-09 20:03         ` Alan Cox

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