Re: Architectural implications of locate mode I/O

Lawrence D'Oliveiro wrote:

On Tue, 02 Jul 2024 17:36:50 -1000, Lynn Wheeler wrote:
 

When doing IBM's HA/CMP and working with major RDBMS vendors on cluster
scaleup in late 80s/early 90s, there was lots of references to POSIX
light-weight threads ...

 Threads were all the rage in the 1990s. People were using them for
everything. One language (Java) absorbed threading right into its core DNA
(where is the locking API? Oh, it’s attached to the base “Object” type
itself!).
 People backed off a bit after that. Nowadays we see a revival of the
“coroutine” idea, where preemption only happens at explicit “await”
points. For non-CPU-intensive workloads, this is much easier to cope with.
 

... and asynchronous I/O for RDBMS (with no buffer > copies) and the
RDBMS managing large record cache.

 This is why POSIX has the disk-oriented “aio” API, for the diehard DBMS
folks. Linux also added “io_uring”, for high performance but not disk-
specific I/O.

Really old PC printers (dot matrix or similar) still had a line buffer worth of on-device memory, enough so that the CPU could sit in a buzy loop sending bytes over the Centronix interface until it got the "I'm full" status bit back, or N bytes had been sent. At that point my disk spooler code would back off and let the next timer interrupt check to see if there was both more print data to be sent and the printer signalled that it was ready to receive more data.
The original serial ports had no buffer at all, so you had to use interrupts for both sending and receiving if you wanted to do anything else while communicating. Around 1984 the serial ports gained a 16-byte buffer, so at that time it made sense to use a hybrid approach, filling/emptying the buffer on each interrupt, while reducing the interrupt load by an order of magnitude.
I.e. acting somewhat like a channel program, but using the main/only cpu to do all the work in the background.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"