Date: Wed, 02 Apr 2003 17:23:41 -0800 From: Peter Wemm <peter@wemm.org> To: Nate Lawson <nate@root.org> Cc: cvs-all@FreeBSD.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: <20030403012341.B55B32A8A7@canning.wemm.org> In-Reply-To: <Pine.BSF.4.21.0304021706050.12767-100000@root.org>
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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!! */
#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.
> -Nate
>
Cheers,
-Peter
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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