Re: [RFC] /sbin/hotplug multiplexor

[Stephen Williams <steve@icarus.com>]

Stephen Williams wrote:
> david-b@pacbell.net said:
> 
>>How often do you connect a new USB or PCI device?  If it takes a full
>>second to react, that's OK; and Linux is usually faster than that.
> 
> 
> When I was running on a 66MHz system w/ 128Meg RAM, it took on
> the order of 30 seconds to get around to invoking fxload. The
> initial execute of /sbin/hotplug may be quick, but that script
> sure takes a while to run. I think performance is an issue.


david-b@pacbell.net said:
> Systems that are "under-powered" have other tools available, like
> having /sbin/hotplug be a custom C program.  Hmm, where have I heard
> of such a thing before, Greg?  :) 

OK, temper-tantrum follows...

A CPU is pegged in my K-WizzyHz workstation doing a Verilog simulation
or some image processing, and I hotplug a camera to get more images.
Now /sbin/hotplug starts running a bunch of processes, causing a lot
of kernel activity to dispatch the hotplug event to umpteen processes,
fiddling with a zillion minor configuration files and subscripts until
it gets figured out and a kernel module for a USB mass storage device
is loaded, all the while thrashing caches and invoking page allocations-
deallocations, and disrupting the background task, not to mention the
desktop.

A ridiculous burden is a ridiculous burden no matter how fast the
host system. I want my super-system doing *my* work, not spending
barrels of mips and I/O cycles picking its nose.

I used my earlier mentioned 66MHz system to receive high resolution
8.5x11" color images, several images per second; yet plugging in a
minor USB device was a major disruption for half a minute. Something
is very wrong with this picture.

Incidentally, with REMOVER support, unplugging that minor device
was nearly instantaneous on this "under-powered" machine. So getting
the event to a process and dispatching it should be fast. It's been
a while since I've been in the guts of the hotplug scripts, but my
impression remains that they are in desperate need of diet, even
for the normal case.


-- 
Steve Williams                "The woods are lovely, dark and deep.
steve at icarus.com           But I have promises to keep,
steve at picturel.com         and lines to code before I sleep,
http://www.picturel.com       And lines to code before I sleep."




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