Subject: Re: Is the netBSD kernel Preemptible ?
To: None <tech-perform@NetBSD.ORG>
From: Gary Thorpe <firstname.lastname@example.org>
Date: 06/14/2002 21:13:06
>From: email@example.com (Greg A. Woods)
>Reply-To: tech-perform@NetBSD.ORG (NetBSD Performance Technical Discussion
>To: NetBSD Performance Technical Discussion List <tech-perform@NetBSD.ORG>
>Subject: Re: Is the netBSD kernel Preemptible ?
>Date: Fri, 14 Jun 2002 20:25:12 -0400 (EDT)
>That's from "Multiprocessor UNIX Operating Systems" in the Oct. 1984
>edition of the BSTJ.
>They do say that I/O bound jobs don't do quite so well as CPU bound jobs
>(which with their state of the art were running at 1.7 times the
>throughput on a two-CPU system as on a single CPU system). Still I'd
>like to see some numbers on modern hardware before I would go so far as
>to admit that MP-specific driver coding is really worth the effort.
In a very hyped "showdown" between Linux and Windows NT on web serving
performance, Windows NT gained a great throughput advantage in the SMP
configuration because Linux was unable to allow multiple threads to use the
multiple network adapters in the machine very efficiently (unfortunately I
have no links/references).
Apparently they fixed this, but what I think of is this: they had to
basically "wait-and-see" to find out what parts were not taking advantage of
SMP. Basically, there is such a large volume of code in a monolithic kernel
to "fix", you cannot reasonably expect to catch even fairly important
sections which need rewritting. Since NetBSD eventually hopes to become
SMP-capable, what plans are there to prevent this?
>The driver entry points are obviously very well known by the kernel.
>They're identical for all drivers. Even in *BSD this part of the device
>driver API is _very_ well defined. The kernel really cannot call a
>driver routine that it doesn't already know about!
Do you mean: open(), read(), write(), ioctl(), etc? What about routines
which are not for user-space, e.g. routines used by these access points to
do the grunt work? Won't each driver need to lock/coordinate access?
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