Re: Active waiting with yield()

[Mikulas Patocka <mpatocka@redhat.com>]

On Tue, 18 Nov 2008, Alan Cox wrote:

> > This makes a code branch that is very rarely tested and a potential bug. 
> > Every such rarely executed branch is a danger and even a silly typo in the 
> > code can hide there for many years without being noticed.
> 
> Learn to use a debugger. You want an unusual timing to occur you
> breakpoint the relevant task and suspend it for a bit.
> 
> > So, I say msleep(1) instead of yield(). What are the counterarguments to 
> > msleep?
> 
> msleep isn't particularly a problem. You are giving up the CPU and not
> wasting so much power and you won't deadlock in realtime. Assuming you
> only expect one or two msleep cycles its fine.

So msleep(1) should be OK. I can't think of a case when it could break.

> And if you think virtualisation and power management and correctness
> (as Ingo noted) are a "bad reason" you need to wake up to the real world.

If the involved cases are:
- a race condition that never happened to a user, only seen during 
artifical testing
- a race condition that existed for 5 years and just one user hit it

--- then yes, considering power management is a bad reason.

Mikulas

> Alan
>