Date: Tue, 7 Aug 2001 09:55:09 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Terry Lambert <tlambert2@mindspring.com> Cc: Mike Smith <msmith@freebsd.org>, Zhihui Zhang <zzhang@cs.binghamton.edu>, freebsd-hackers@freebsd.org Subject: Re: Allocate a page at interrupt time Message-ID: <200108071655.f77Gt9M32808@earth.backplane.com> References: <200108070739.f777dmi08218@mass.dis.org> <3B6FB0AE.8D40EF5D@mindspring.com>
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:> > It also has the unfortunate property of locking us into virtual
:> > wire mode, when in fact Microsoft demonstrated that wiring down
:> > interrupts to particular CPUs was good practice, in terms of
:> > assuring best performance. Specifically, running in virtual
:> > wire mode means that all your CPUs get hit with the interrupt,
:> > whereas running with the interrupt bound to a particular CPU
:> > reduces the overall overhead. Even what we have today, with
:> > the big giant lock and redirecting interrupts to "the CPU in
:> > the kernel" is better than that...
:>
:> Terry, this is *total* garbage.
:>
:> Just so you know, ok?
:
:What "this", exactly?
:
:That "virtual wire" mode is actually a bad idea for some
:applications -- specifically, high speed networking with
:multiple gigabit ethernet cards?
All the cpu's don't get the interrupt, only one does.
:That Microsoft demonstrated that wiring down interrupts
:to a particular CPU was a good idea, and kicked both Linux'
:and FreeBSD's butt in the test at ZD Labs?
Well, if you happen to have four NICs and four CPUs, and
you are running them all full bore, I would say that
wiring the NICs to the CPUs would be a good idea. That
seems like a rather specialized situation, though.
-Matt
:That taking interrupts on a single directed CPU is better
:than taking an IPI on all your CPUs, and then sorting out
:who's going to handle the interrupt?
:...
:
:-- Terry
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