Messages in this thread | | | Date | Sat, 16 Mar 2002 18:54:21 -0700 | From | yodaiken@fsmlabs ... | Subject | Re: 2.4.18 Preempt Freezeups |
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On Sun, Mar 17, 2002 at 02:14:14AM +0100, Daniel Phillips wrote: > On March 17, 2002 02:13 am, yodaiken@fsmlabs.com wrote: > > On Sun, Mar 17, 2002 at 01:33:04AM +0100, Daniel Phillips wrote: > > > On March 16, 2002 01:40 am, yodaiken@fsmlabs.com wrote: > > > > > > > > Without preempt: > > > > x = movefrom processor register; > > // if preemption is on, we can be preempted and restart > > // on another processor so x will be wrong > > > > do_something with x > > > > > > > > is safe in SMP > > > > With [preempt] it requires a lock. > > > > > > It must be a trick question. Why would it? > > > > See comment. > > Which processor register were you thinking of? Surely not anything in the > general register set, and otherwise, it's just another example of per-cpu > data. It needs to be protected, and the protection is lightweight.
So what didn't you understand? Your (dubious) assertion that the lock is "lightweight" has absolutely no bearing on whether a lock is needed or not.
> > -- > Daniel
-- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com
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