Performance of write(2) based on size and alignment of user data

Performance of write(2) based on size and alignment of user data

Post by Mark R. Ludw » Thu, 31 Oct 1991 07:16:12

When writing data to a file with write(2), what are the performance
options?  It seems that if the data is one or more whole pages and is
aligned on a page boundary, that the user application expends fewer
cycles to write the data.  Can someone explain some of the variations
on this theme?  For example, are both the alignment and size
important, or is it just the alignment?

I have the understanding that there is a temp*aspect to the
performance gain because the performance improvement results from the
kernel playing games with the page map: while I/O is in progress the
page is in fact not in my address space any more.  If I reference any
byte in the page of interest, I cause a page fault which effectively
nullifies the original performance gain.  Am I correct, or is the gain
achieved some other way?

How much of this varies with the vendor?  We seem to get a bigger gain
on our BSD systems.  Is there something different about BSD, or should
we see the same thing on AT&T Unix too?

This is one of the few times I wish we had sources.$$

USPS: 3625 Del Amo Boulevard, Suite 370, Torrance, CA  90503
UBM2: MVS may be slow, but it _sure_ is hard to use.


1. Howto grab data from a 3270 screen and write data into it with script based software?

I need a 3270 terminal software which should connect to an IBM mainframe.

Certain data fields on the 3270 screen should then be grabbed/fetched into e.g. a local
file and other data should be filled into other fileds on the 3270 screen/terminal.

Does someone know such a software?

Again: I am not only searching for a dumb 3270 terminal emulator but for a 3270 software
which allows (script based) interacting from local system to the remote screen.

Any idea is appreciated.


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