Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!udel!mmdf
From: Glen Lalonde <lalonde@torolab2.vnet.ibm.com>
Newsgroups: comp.os.minix
Subject: Better performance for 68K based minix?
Message-ID: <51458@nigel.ee.udel.edu>
Date: 22 Apr 91 02:09:08 GMT
Sender: mmdf@ee.udel.edu
Lines: 30

I found a message from way back in 89 about how to patch FS to call
phys_copy directly thus you don't need to send/rec a message from the
kernel to do the copy. Later the person indicated this patch did not work
because the process may be shadowed. So I went about doing the same type of
thing but this time with a fix to the shadow problem. FS gets informed when
a fork happened, thus it knows which processes are shadowed. All you need to
do is tell it when a exec occures. I modified the fproc table in fs to have
an entry which indicates the process may be shadowed. In the fork processing
of FS I set the bit true for the child and father. And now I have MM send
a message to FS telling it when/who did a exec. At which point FS reset
the bit in the fproc table. This does work in most cases, but not for the
shell since it forks, child execs. Which will have the child set to no
shadow but not the shell. No big deal most processes fork/exec.

Anyways, what I do in FS rw_user is check the bit and call phys_copy
if I know the process is not shadowed. This will reduce the number of
messages by 2, from 4 or 6. See page 184 of the book. I did hope for
a 5-15% decrease in time for reads/writes. I tried to measure the
decrease by using about 10 lines of
dd if=/dev/ram of=/dev/null bs=1024 count=500, in a shell then doing
'time' on the shell. What this showed was a decrease in user time from
8.0 to 4.5 BUT an increase in sys time from 1:18.0 to 1:21.0 or so.
I really don't understand this, the copy is done in FS not kernel but
both get rolled up in sys time.(correct?) Thus why the change? Is there
a better way to measure this? BTW, real time was constant over the two
cases both giving about 1:26.0

I am using MacMinix with a GCC compiled mm and fs.