Subject: Re: But why?
To: Miguel de Icaza <firstname.lastname@example.org>
From: Jason Thorpe <email@example.com>
Date: 10/24/1996 02:29:18
On Wed, 23 Oct 1996 22:53:15 -0500
Miguel de Icaza <firstname.lastname@example.org> wrote:
> Besides, we do not measure getpid (), we measure read()ing 1 byte from
> a null device.
Couple of obvious flaws:
- When you take a measurement of this test on different
types of OSes, you're not necessarily measuring the
same thing. Not only are you not measuring simple
system-call overhead (which is what this whole
thing is about anyhow, right?), but different systems
may have different layering techniques which produce
- Even if the results are `poor' (which, in this crowd,
is defined as `slower that Linux', I guess), your
measurement may not be an indication of deterimental
impact on the system overall.
- Just who reads one $#^% byte, anyhow? System calls like
that are typically `optimized' for larger transactions,
like MAXPHYS (64k under BSD).
So, you're not testing the more common case. Now, if you were to
test the common case, using a `NULL device' (I'm assuming /dev/null)
isn't fair, because to implement it, all you have to do is set resid
to 0 and return. Indeed, to actually measure read() you have to copy
something to the user's address space.
Jason R. Thorpe email@example.com
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