Messages in this thread | | | Date | Tue, 8 May 2007 09:47:51 -0700 (PDT) | From | david@lang ... | Subject | Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11 (PCI_MULTITHREAD_PROBE) |
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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?
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