how to use wait_event_interruptible_timeout with less than 1 jiffie timeout?

[Nicholas Mc Guire]

On Wed, Jan 20, 2016 at 11:50:24AM +0530, Anupam Kapoor wrote:
> 
> >>>>> [2016-01-20T01:21:18+0530]: "Daniel." (Daniel):
> ,----[ Daniel ]
> | I have some code that convert an timeout comming from userspace (in
> | ms) to jiffies prior passing to wait_event_interrupitible_timeout().
> | The code looks like this:
> | 
> | unsigned long tout = user.timeout * HZ / 1000; /* convert from ms to jiffie */

that should be a  unsigned long tout = msecs_to_jiffies(user.timeout);

to ensure that all corner cases are properly handled, e.g. for HZ=100 the
above would be 0 for user.timeout < 10 which is probably not what you want.

> | int status = wait_event_interruptible_timeout(wq, cond, tout);
> | 
> | I'm using HZ=100, the known default.
> | The problem is: with HZ = 100 and user.timeout = 10 I have:
> | 10 * 100 / 1000 = 1,
> | 
> | This means that I can't use timeouts with less than 10ms. Is there any
> | way to circunvent this without changing HZ value?
> `----
> wouldn't msleep_interruptible(...) be a better choice ? as a bonus, it
> takes care of jiffies wrapping etc. 
> 

that would still have the same limitation with resepct to time granuarlity
and as Documentation/timers/

if you really need very short delays then you will need to resort to hrtimers
(and thus be to some extent config dependent) usleep_range(min, max) is the 
prefered interface in that case.

thx!
hofrat