Date: Thu, 3 Apr 2003 14:24:44 -0500 From: Andrew Gallatin <gallatin@cs.duke.edu> To: Peter Wemm <peter@wemm.org> Cc: Nate Lawson <nate@root.org> Subject: Re: 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 ... Message-ID: <20030403142444.A32536@grasshopper.cs.duke.edu> In-Reply-To: <20030403012341.B55B32A8A7@canning.wemm.org>; from peter@wemm.org on Wed, Apr 02, 2003 at 05:23:41PM -0800 References: <Pine.BSF.4.21.0304021706050.12767-100000@root.org> <20030403012341.B55B32A8A7@canning.wemm.org>
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Peter Wemm [peter@wemm.org] wrote:
> Nate Lawson wrote:
<..>
> > 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!! */
> #ifdef SWTCH_OPTIM_STATS
> else
> stupid_switch++;
> #endif
>
> 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.
I think alpha has this feature:
LEAF(cpu_switch, 1)
<..>
CALL(choosethread) /* can't return NULL */
mov v0, s2 /* s2 = new thread */
ldq s3, TD_MD_PCBPADDR(s2) /* s3 = new pcbpaddr */
/*
* Check to see if we're switching to ourself. If we are,
* don't bother loading the new context.
<..>
cmpeq s0, s2, t0 /* oldthread == newthread? */
bne t0, Lcs7 /* Yes! Skip! */
Drew
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