Messages in this thread |  | | | From | Daniel Phillips <> | | Subject | Re: 2.4.18 Preempt Freezeups | | Date | Sun, 17 Mar 2002 03:08:06 +0100 |
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On March 17, 2002 02:54 am, yodaiken@fsmlabs.com wrote: > 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.
I didn't understand which kind of register you meant (because you didn't say). For the bog-standard variety I don't see a problem.
Protection of special registers is lightweight, it's just a preempt disable/enable (inc/dec).
-- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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