Messages in this thread | | | Date | Sun, 9 Mar 2008 11:36:01 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v2] add time_now_after and other macros which compare with jiffies |
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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.
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