*BAD* impact of usb on PCI performance
Hi!
I did some testing how does usb hurt rest of system; and it can be pretty bad.
With Acher's uhci, even ifconfig up of usb-to-usb networking device [plusb handled by generic usb-to-usb driver; see -ac series]. does 50% slowdown. When fsbr is being used, systems slows down by 350% (running more than 4 times slower than normally. Ouch).
Pavel
2.4.5: 300MHz, no usb at all (compiled out)
0.06user 3.25system 3.30 (0m3.308s) elapsed 100.00%CPU 0.06user 3.25system 3.30 (0m3.307s) elapsed 100.00%CPU 0.03user 3.28system 3.32 (0m3.323s) elapsed 99.61%CPU 2.4.5: 300MHz, usb ifconfig down [acher]
0.05user 3.28system 3.35 (0m3.357s) elapsed 99.18%CPU 0.03user 3.29system 3.31 (0m3.319s) elapsed 100.00%CPU 0.04user 3.29system 3.32 (0m3.325s) elapsed 100.00%CPU 0.01user 3.32system 3.32 (0m3.326s) elapsed 100.00%CPU 2.4.5: 300MHz, usb not plugged [JE]
0.06user 3.24system 3.30 (0m3.303s) elapsed 99.90%CPU 0.06user 3.25system 3.30 (0m3.304s) elapsed 100.00%CPU 0.02user 3.30system 3.33 (0m3.336s) elapsed 99.52%CPU 2.4.5: 300Mhz, plusb loaded and UP [acher]
0.03user 4.93system 4.99 (0m4.993s) elapsed 99.33%CPU 0.02user 4.94system 4.99 (0m4.991s) elapsed 99.37%CPU 0.04user 4.92system 4.99 (0m4.990s) elapsed 99.40%CPU 0.06user 4.90system 4.98 (0m4.985s) elapsed 99.49%CPU 0.04user 4.91system 4.98 (0m4.983s) elapsed 99.33%CPU 0.05user 4.91system 4.98 (0m4.985s) elapsed 99.50%CPU 0.06user 4.90system 4.98 (0m4.989s) elapsed 99.42%CPU 0.06user 4.91system 4.99 (0m4.995s) elapsed 99.49%CPU 2.4.5: 300Mhz, plusb plugged in [JE]
0.03user 3.29system 3.35 (0m3.352s) elapsed 99.05%CPU 0.02user 3.29system 3.34 (0m3.349s) elapsed 98.85%CPU 0.01user 3.30system 3.34 (0m3.349s) elapsed 98.84%CPU 2.4.5: 300Mhz, plusb plugged in and UP [JE]
0.04user 3.29system 3.32 (0m3.327s) elapsed 100.00%CPU 0.02user 3.31system 3.35 (0m3.356s) elapsed 99.23%CPU 0.04user 3.28system 3.35 (0m3.353s) elapsed 99.03%CPU 2.4.5: 300Mhz, plusb loaded and UP, fsbr forced ON [acher] 0.06user 14.39system 14.54 (0m14.542s) elapsed 99.37%CPU 0.03user 14.51system 14.62 (0m14.625s) elapsed 99.42%CPU 0.04user 14.63system 14.79 (0m14.798s) elapsed 99.14%CPU 2.4.5: 300Mhz, plusb loaded and UP, fsbr forced ON [JE] 0.04user 14.87system 14.98 (0m14.986s) elapsed 99.49%CPU 0.06user 14.85system 14.99 (0m14.994s) elapsed 99.43%CPU 0.04user 14.85system 14.98 (0m14.984s) elapsed 99.37%CPU
Signature · 2 lines
I'm [email protected]. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at [email protected]
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From: "Georg Acher" <[email protected]>
Quoted 4 lines · Pavel Machek
With Acher's uhci, even ifconfig up of usb-to-usb networking device [plusb handled by generic usb-to-usb driver; see -ac series]. does 50% slowdown. When fsbr is being used, systems slows down by 350%
Hm, the 50% make me curious... have to look what's happening...
For PL-2301/2302 devices, "ifconfig up" is mostly just posting a bulk read. True with both "usbnet" and its (now obsolete) predecessor drivers "plusb" and (for different devices) "net1080".
Laplink-style cables can often support another mode (poll via USB "interrupts", and then issue reads only when data is available) but not every device can work that way (like, I seem to recall, an iPaq PDA). And that'd increase the latency per packet by a couple milliseconds, even when it's possible.
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(running more than 4 times slower than normally. Ouch).
Blame Intel. Either low latency or low PCI usage, you can choose...
This problem is UHCI-specific, not USB-generic, yes? Doesn't happen with OHCI?
- Dave