| Author |
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Jim Stewart
Guest
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 Posted:
Wed Feb 16, 2005 2:28 am Post subject:
Re: Self restarting property of RTOS-How it works? |
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Tim Wescott wrote:
| Quote: | CBFalconer wrote:
Already done, in the tall buildings. There the problem is to
conserve elevator shaft space. Works something like airline hubs
and feeder lines.
And I've seen proposals (still in the gee-whiz) stage to have an "up"
shaft, a "down" shaft and a few cross-shafts, with motors in the
elevator cars so they have more autonomy for getting up and down.
It was a popular science kind of thing -- I have no idea if it's being
seriously developed (but it'd be fun to do the software!).
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Google "wonkavator" (: |
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Stephen Fuld
Guest
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| Posted:
Wed Feb 16, 2005 4:44 am Post subject:
Re: Self restarting property of RTOS-How it works? |
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"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:421237FB.FB33D465@yahoo.com...
| Quote: | Stephen Fuld wrote:
"Nick Maclaren" <nmm1@cus.cam.ac.uk> wrote in message
CBFalconer <cbfalconer@yahoo.com> writes:
I would expect better algorithms would await better input methods.
For example, instead of selecting from 'up' or 'down', the
prospective rider could select the destination floor. Now an
arriving car has to display which floors it will handle, and
separate the sheep from the goats. The sheep and goats have to be
sufficiently alert to be separated. Maybe something along the
lines of "take a ticket" based on rfids would work.
Yes. As with all such issues, a very small amount of extra
information can make a great deal of difference.
The key word here is "can". In thinking about this particular
possibility, it seems the big advantage would be if one could have
multiple elevators where one would service the "higher" floors and
one the "lower". Then the people going to the higher ones wouldn't
have to wait for all the stops in the lower ones. This is probably
only usefull for fairly tall buildings. In fact, for such
buildings, something like this is frequently done. I have been in
buildings with multiple banks of elevators each clearly labeled
with the range of floors they service. While this doesn't have the
flexibility of being able to change the floors serviced
dynamically, it avoids the need for dynamic "sheep/goat
separation", (with presumably a higher mistake rate than a static
system) as described above.
Already done, in the tall buildings. There the problem is to
conserve elevator shaft space. Works something like airline hubs
and feeder lines.
|
That is a different solution. What you are talking about is "stacked"
elevators, where you have to get off at some intermediate floor and switch
to another elevator. That is the only way to conserve shafts. What I was
talking about was where all the elevators went to the lobby, but only to a
subset of the upper floors. Doesn't conservve shafts, but reduces total
time for those wanting to go to the upper floors, as they don't have to wait
through all the stops on the lower ones.
--
- Stephen Fuld
e-mail address disguised to prevent spam |
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del cecchi
Guest
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| Posted:
Wed Feb 16, 2005 7:55 am Post subject:
Re: Self restarting property of RTOS-How it works? |
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"Stephen Fuld" <s.fuld@PleaseRemove.att.net> wrote in message
news:sPvQd.219436$w62.163678@bgtnsc05-news.ops.worldnet.att.net...
snip
| Quote: |
That is a different solution. What you are talking about is "stacked"
elevators, where you have to get off at some intermediate floor and
switch
to another elevator. That is the only way to conserve shafts. What
I was
talking about was where all the elevators went to the lobby, but only
to a
subset of the upper floors. Doesn't conservve shafts, but reduces
total
time for those wanting to go to the upper floors, as they don't have
to wait
through all the stops on the lower ones.
--
- Stephen Fuld
e-mail address disguised to prevent spam
But doesn't queuing theory, a branch of mathematics and maybe |
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)? Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
del
newsgroups trimmed |
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Stephen Sprunk
Guest
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| Posted:
Wed Feb 16, 2005 7:55 am Post subject:
Re: Self restarting property of RTOS-How it works? |
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"del cecchi" <dcecchi.nojunk@att.net> wrote in message
news:37fs81F5d1b7vU1@individual.net...
| Quote: | But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)?
|
That might depend on traffic patterns. Most trips are to/from the lobby or
mezzanine, so multiple queues and servers may perform better. As common as
the multiqueue design is in tall buildings, one must assume it's closer to
optimal in practice than a single-queue system. Individuals may be
incompetent, but rarely entire industries.
| Quote: | Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
|
That is a problem in some buildings, but many have a single overlapping
floor; to go from 20 to 10 you would change at, say, 15 instead of the
lobby. The overlapping floor is usually omitted from the signage for one of
the banks down in the lobby, but the other floors will be signed correctly.
I've also seen stacked systems where there are additional lobbies on the
higher levels, and only those lobbies are reachable from the ground floor.
Upon reaching the upper lobby, you sign in (or wave a badge) to get access
to a different bank that serves the various floors for that company.
S
--
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin |
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Jan Vorbrüggen
Guest
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| Posted:
Wed Feb 16, 2005 1:08 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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| Quote: | I would expect better algorithms would await better input methods.
For example, instead of selecting from 'up' or 'down', the
prospective rider could select the destination floor.
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I've been in two buildings in recent years where the elevator user interface
works just in that way. One is ~30 stories, but the other is only 14, IIRC.
Both have access control via RFID cards, and those cards can be programmed
to either just allow a single floor - no need to enter the data then - or
a range of floors. Once the desired floor has been entered (explicitly or
implicitly), the display will show the letter of the elevator that will
service you. For larger parties, it is recommended to enter the data more
than once.
Jan |
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Sander Vesik
Guest
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| Posted:
Wed Feb 16, 2005 1:22 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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In comp.arch Del Cecchi <cecchinospam@us.ibm.com> wrote:
| Quote: | Ed Beroset wrote:
Terje Mathisen wrote:
I have noted previously here in c.a that most of the _really_ good
low-level/systems programmers I know seem to have an engineering
instead of computer science background.
A coincidence?
I have also noticed that the programmers from a computer science
background tend to be much better at working out a system architecture
and planning first.
My hypothesis: the more detail-oriented people tend to gravitate toward
the engineering side, and tend to excel at detail-oriented tasks, while
the computer science people tend to be better at big picture and
abstract concepts.
Just MHO.
Ed
Those comp-sci geniuses are the ones that gave us a software paradigm
that is susceptible to attacks as simple as buffer overruns, and store
data in randomly scattered chunks linked by pointers. And put multiple
unrelated locks in the same cache line? That the ones you are talking
about?
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Compared to the quality of say the "average" ethernet controller
out there these don't seem to be all that major bloopers?
--
Sander
+++ Out of cheese error +++ |
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Nick Maclaren
Guest
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| Posted:
Wed Feb 16, 2005 3:06 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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In article <1108524628.132798f1452d823327c1ece4e24c95bc@teranews>,
Stephen Sprunk <stephen@sprunk.org> wrote:
| Quote: | "del cecchi" <dcecchi.nojunk@att.net> wrote in message
news:37fs81F5d1b7vU1@individual.net...
But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)?
That might depend on traffic patterns. Most trips are to/from the lobby or
mezzanine, so multiple queues and servers may perform better. As common as
the multiqueue design is in tall buildings, one must assume it's closer to
optimal in practice than a single-queue system. Individuals may be
incompetent, but rarely entire industries.
|
A clearer way to think about it is to ask what you mean by "better"
and exactly what the constraints are. Yes, for total throughput
and a fixed total capacity, the naive analysis is right. That is
not always the problem that needs to be solved.
Again, just like interconnects :-)
Regards,
Nick Maclaren. |
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Bernd Paysan
Guest
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| Posted:
Wed Feb 16, 2005 6:59 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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Nick Maclaren wrote:
| Quote: | |> You might imagine that a clever 10yo boy made certain that the
|> elevator's path was the most convoluted possible. My sisters weren't
|> much better.
Could you overload its memory?
|
The funny thing is that the standard elevator algorithm needs only one bit
per level, and an additional bit for the direction, i.e. less than this
FIFO algorithm. The bit per level is used anyway (to light the pressed
buttons), and the direction bit also can be displayed.
The elevator I used when I was a kid could drive only to the first button
pressed, and it accepted this single command only after the door was closed
- it didn't remember any other button presses. Leaves the scheduling open
to those inside the elevator, and was 100% 10yo proof ;-).
--
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://www.jwdt.com/~paysan/ |
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Nick Maclaren
Guest
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| Posted:
Wed Feb 16, 2005 7:03 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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In article <p60ce2-85p.ln1@miriam.mikron.de>,
Bernd Paysan <bernd.paysan@gmx.de> writes:
|>
|> The elevator I used when I was a kid could drive only to the first button
|> pressed, and it accepted this single command only after the door was closed
|> - it didn't remember any other button presses. Leaves the scheduling open
|> to those inside the elevator, and was 100% 10yo proof ;-).
Nah. The 10 year-old happily presses buttons moving the lift
between floors 99 and 100, while those on the ground floor
are wondering how long it will taken them to climb the stairs.
Regards,
Nick Maclaren. |
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Bernd Paysan
Guest
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| Posted:
Wed Feb 16, 2005 7:17 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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CBFalconer wrote:
| Quote: | Already done, in the tall buildings. There the problem is to
conserve elevator shaft space. Works something like airline hubs
and feeder lines.
|
The WTC AFAIK had two sorts of elevators: express ones, which could go up to
levels divided by 20 or so (each of them single source/single destination,
so that the elevators took less from the office space in the precious upper
floors), and slower ones, which shared the shaft space, and could only
reach up within the express lift granularity. To use the vertical space
even better, it could be possible to have a several-level express lift,
i.e. with entrances in several levels, but still with the +-20 floors (or
whatever) granularity.
If I was to build a skyscraper, I would build a big, fast, several-level
wide-granularity express elevator (a "vertical subway") in the core of the
building, complete with own air supply and water coolant for fire emergency
use, and the slow elevators as panorama elevators on the outside. That way,
no shaft space is used for the slow elevators (all elevator doors are
windows when no elevator is there).
--
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://www.jwdt.com/~paysan/ |
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Bernd Paysan
Guest
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| Posted:
Wed Feb 16, 2005 7:24 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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Nick Maclaren wrote:
| Quote: |
In article <p60ce2-85p.ln1@miriam.mikron.de>,
Bernd Paysan <bernd.paysan@gmx.de> writes:
|
|> The elevator I used when I was a kid could drive only to the first
|> button pressed, and it accepted this single command only after the door
|> was closed - it didn't remember any other button presses. Leaves the
|> scheduling open to those inside the elevator, and was 100% 10yo proof
|> ;-).
Nah. The 10 year-old happily presses buttons moving the lift
between floors 99 and 100, while those on the ground floor
are wondering how long it will taken them to climb the stairs.
|
Well, the elevator took commands from inside only when the door was closed,
but it took commands from outside even when the door was open (I don't know
if it used FIFO or elevator or whatever). So you still had a good chance to
call the 10yo down to ground floor. A DDoS attack (with several 10yo in
several floors) could have been possible, though, but with an elevator
algorithm, it would not do that much harm.
--
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://www.jwdt.com/~paysan/ |
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Alex Colvin
Guest
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| Posted:
Wed Feb 16, 2005 8:51 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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| Quote: | But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)? Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
|
All other things being equal, yes. Likewise, Cell should have symmetric
processors.
But a hub system makes sense when other things aren't equal. And
dedicated coprocessors have their uses.
--
mac the naďf |
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Stephen Fuld
Guest
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| Posted:
Wed Feb 16, 2005 10:18 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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"del cecchi" <dcecchi.nojunk@att.net> wrote in message
news:37fs81F5d1b7vU1@individual.net...
| Quote: |
"Stephen Fuld" <s.fuld@PleaseRemove.att.net> wrote in message
news:sPvQd.219436$w62.163678@bgtnsc05-news.ops.worldnet.att.net...
snip
That is a different solution. What you are talking about is "stacked"
elevators, where you have to get off at some intermediate floor and
switch
to another elevator. That is the only way to conserve shafts. What
I was
talking about was where all the elevators went to the lobby, but only
to a
subset of the upper floors. Doesn't conservve shafts, but reduces
total
time for those wanting to go to the upper floors, as they don't have
to wait
through all the stops on the lower ones.
--
- Stephen Fuld
e-mail address disguised to prevent spam
But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)?
|
As others have said, it depends upon the request pattern. The math you
mention assumes things like randonly distributed service times. But that is
not the case here, as the service time of a higher floor is almost certainly
higher than that for a lower floor, so a request for a higher floor gets a
different distribution of service time than one for a lower floor. Think of
the situation in a super market with express lines for a limited number of
items. That is clearly a better solution even though it separates the
servers into two classes.
| Quote: | Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
|
Or some "intermediate" floor that is serviced by both banks. But such trips
are relativly rare and compared to the savings on trips from the lobby to
the higher floors, which are much more common, it is a worthwhile tradeoff.
--
- Stephen Fuld
e-mail address disguised to prevent spam |
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Eric P.
Guest
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| Posted:
Wed Feb 16, 2005 10:57 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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Stephen Fuld wrote:
| Quote: |
"del cecchi" <dcecchi.nojunk@att.net> wrote in message
news:37fs81F5d1b7vU1@individual.net...
But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)?
As others have said, it depends upon the request pattern. The math you
mention assumes things like randonly distributed service times. But that is
not the case here, as the service time of a higher floor is almost certainly
higher than that for a lower floor, so a request for a higher floor gets a
different distribution of service time than one for a lower floor. Think of
the situation in a super market with express lines for a limited number of
items. That is clearly a better solution even though it separates the
servers into two classes.
Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
Or some "intermediate" floor that is serviced by both banks. But such trips
are relativly rare and compared to the savings on trips from the lobby to
the higher floors, which are much more common, it is a worthwhile tradeoff.
|
It also depends on what you are trying to optimize. Remember you
are not the elevator company's customer - the building owner is.
They might want to optimize energy expenditure. After a request is
made you wait 10 seconds before dispatching to accumulate requests.
Or optimize throughput volume for different times of the day.
For morning you stage cars at the first floor.
For 12:00 and 5:00 you stage in the middle and top.
Or minimize wait time. Just a guess but I'll bet that
optimizing throughput is not the same as minimizing wait time.
One building I know of sold preferred elevator service to tenants.
For preferred clients you stage near them.
I believe modern cars also have weight sensors. You should
change your plan if a bunch of people fill the car at one floor.
Eric |
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Del Cecchi
Guest
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| Posted:
Thu Feb 17, 2005 7:08 pm Post subject:
Re: Self restarting property of RTOS-How it works? |
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Alex Colvin wrote:
| Quote: | But doesn't queuing theory, a branch of mathematics and maybe
engineering, say that rather than having multiple queues and multiple
servers (elevators dedicated to a floor or floors) that it is better to
have a single queue and multiple servers (all elevators serving all
floors)? Besides, does that mean that to go from 20 to 10 you have to
go to the lobby? yuck.
All other things being equal, yes. Likewise, Cell should have symmetric
processors.
But a hub system makes sense when other things aren't equal. And
dedicated coprocessors have their uses.
|
Why do say it "should have symmetric processors"? Isn't it better to
have specialized processors if the workload is known? After all, no one
says it would be better if GPUs were replaced with Opterons, eh?
del |
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