cvs commit: src/sys/conf options.i386 src/sys/i386/i386 machdep.c mp_machdep.c pmap.c swtch.s src/sys/i386/include md_var.h pmap.h smp.h src/sys/i386/isa apic_vector.s intr_machdep.h src/sys/kern kern_switch.c kern_synch.c kern_thr.c kern_thread.c subr_witness.c ...

Peter Wemm peter at
Wed Apr 2 17:23:43 PST 2003

Nate Lawson wrote:
> On Wed, 2 Apr 2003, Peter Wemm wrote:
> >   Commit a partial lazy thread switch mechanism for i386.  it isn't as lazy
> >   as it could be and can do with some more cleanup.  Currently its under
> >   options LAZY_SWITCH.  What this does is avoid %cr3 reloads for short
> >   context switches that do not involve another user process.
> This is awesome!
> >   One non-trivial change was to select a new thread before calling
> >   cpu_switch() in the first place.  This allows us to catch the silly
> >   case of doing a cpu_switch() to the current process.  This happens
> >   uncomfortably often.  This simplifies a bit of the asm code in cpu_switch
> >   (no longer have to call choosethread() in the middle).  This has been
> >   implemented on i386 and (thanks to jake) sparc64.  The others will come
> >   soon.  This is actually seperate to the lazy switch stuff.
> Shouldn't there be a "if (thread == curthread) return;" in the scheduling
> code somewhere?

There is now. :-)

        newtd = choosethread();
        if (td != newtd)
                cpu_switch(td, newtd);  /* SHAZAM!! */

sparc64's cpu_switch() already optimized this case.  i386 didn't.  I haven't
checked alpha/ia64 yet, but they're still using the old no-args API.

> -Nate

Peter Wemm - peter at; peter at; peter at
"All of this is for nothing if we don't go to the stars" - JMS/B5

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