On Tue, 8 May 2007, Cornelia Huck wrote:
2. Sheer volume of devices on a bus. Even if the indivdual probing
doesn't take long, having all devices probed one after the other may
take a lot of time. Putting the actual probe on a thread makes it
possible to run several probes in parallel, thereby cutting probing
time.
(FWIW, the s390 cio layer does asynchronous probing at the bus level,
where work is usually outstanding for a lot of devices at once. Where a
2.4 kernel might take half an hour to detect all devices, we slashed it
down to half a minute. I believe we could make rescans work even better
with multithreaded probing with some tweaking.)
Threading at the bus level just inevitably means things like random
numbers for devices depending on some timing/scheduling issue. That's
nasty.
Threading at a driver level still does that (ie individual disks may be
attached in some order that depends on how fast they are to respond), but
in a much more controlled fashion, and only for drivers that explicitly
say that they can do it.
How is that better? You still must rely on udev for persistent device
names. And controlling device names in the driver can still be done in
the device driver with multithreaded probing (on s390 ccw, devices
already pop up in a random order, and the dasd driver manages to
conjure up consistent names for those devices that the user specified.)
I have used userspace tools for managing multiple machines that spawn
tasks in parallel on multiple machines and then buffers them per-machine
to display the output of the commands in order, no matter which one
finished first.
for example 'dsh m1,m2 ls /' would always result in
m1 .
m1 ..
.
.
m2 .
m2 ..
.
.
even if m2 finished before m1
why can't the detection be done in parallel, but the regestration of
detected devices be done in order?
David Lang
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
