On Wed, Sep 18, 2002 at 10:38:38AM +0200, Kevin D. Kissell wrote:
> From: "Jun Sun" <email@example.com>
> > On Wed, Sep 18, 2002 at 01:44:57AM +0200, Kevin D. Kissell wrote:
> > >
> > > I'd much prefer something that is simple and processor-local,
> > > even if it may be less optimal in some corner cases. For example,
> > > Why not simply use CP0.Status.CU1 as a "dirty" bit? If it's set
> > > when a process switches out, the FPU state gets saved, and CU1
> > > cleared. If it's not set when a process hits an FP instruction,
> > > CU1 gets set and the context gets loaded. This involves no
> > > access whatever to shared control variables, indeed, it doesn't
> > > even go to memory to make the decision. It will, of course, save
> > > some FP contexts that don't need saving, but it is well behaved
> > > in the cases I care most about - it avoids saving/restoring FPRs
> > > of code that is doing no FP whatsoever, and it ensures that
> > > whenever a thread starts up, whatever CPU its on, its full
> > > context is available to that CPU, no (coherent) questions asked.
> > >
> > This is basically 2) except for dirty bit difference.
> > My current implementaion uses bit:1 in task->used_math flag for
> > "dirty" bit purpose.
> Which is not a property of the CPU, but of the thread,
> meaning that it will be written by one CPU and read by
> another, i.e. there will be MP memory traffic and cache
> interventions/invalidations/misses around the operation.
In all places the task is "current" process. Therefore no inter-processor
Obiviously it is still less desriable than a bit in cpu regiters....