On 31 May 2012 07:55, John Baldwin <j...@freebsd.org> wrote: > On Wednesday, May 30, 2012 6:02:15 pm Adrian Chadd wrote: >> Hi, >> >> I've re-run the test with powerd and sleep state stuff disabled - lo >> and behold, UDP tests are now up around 240-250MBit, what I'd expect >> for this 2 stream 11n device. >> >> So why is it that I lose roughly 80MBit of throughput with powerd and >> C2/C3 enabled, when there's plenty of CPU going around? The NIC >> certainly isn't going to sleep (I've not even added that code.) > > Why do you not expect that? I would try, btw, just disabling powerd for now > and leaving C2/C3 enabled to see if that makes a difference.
I expected it because I didn't know what else is going on. Thanks to your braindumping in this thread, I now have a much better appreciation for the issues here. :-) > As to my first question, with powerd enabled and an otherwise idle machine, > powerd may very well be running your CPU at some rediculously low speed (like > 100 Mhz) pretty much all the time. Do you really think you could push more > than 80 MBit with a 100 MHz CPU? This is with the power connected, so powerd seems to leave the CPU at full speed. I'll have to double-check. > Secondly, just having a lot of CPU isn't enough if you don't have it quickly. > Latency matters, too. Take a look at your C2/C3 info like so: > > dev.cpu.0.cx_supported: C1/3 C2/59 C3/93 > > IIRC, the last number is the number of microseconds the CPU takes to resume > from an interrupt. So, on this box (a Core i5), it can take 93 us after an > interrupt occurs during C3 before the CPU will get around to executing the > first instruction. It might be worse on your machine. Ok. I'll check the latency values when I'm back at home. The default bootup too is to use the ACPI idle routine, Even with powerd disabled and sleep limited to C1, I still see the TSC mismatch issues. I've modified my kernel to default to using spin at bootup. I'll see if this fixes the TSC mismatch when doing KTR traces. Thanks, Adrian _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
