Messages in this thread | | | Subject | Re: [PATCH v5 00/11] serial: 8250: split LPSS to 8250_lpss, enable DMA on Quark | From | Bryan O'Donoghue <> | Date | Sun, 12 Jun 2016 18:13:07 +0100 |
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On Tue, 2016-06-07 at 13:04 +0300, Andy Shevchenko wrote: > > I'll find some time to look at both a short stream and a long > stream, > > based on the branch you've indicated and maybe against the latest > > stable kernel. > > Please, do. I'm planning to resend new version soon (this week or > lately beginning of the next one).
So.
Generally DMA appears to make little-to-no difference here. With small data sets, 128 bytes in the test case - there appears to be a slight performance gain at lower BAUD rates, however for small data-sets and large data sets 32k for the large test case, there appears to be a performance penalty at higher BAUD rates.
One thing I have noticed is that the following never completes and can't be reset back to mode=0 or mode=3 to restore functionality - definitely worth looking at if you are spinning another patch.
### never completes #### root@galileo:~# echo 1 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# stty -F /dev/ttyS0 921600 root@galileo:~# time cat tester.txt > /dev/ttyS0 ### never completes ####
Performance data set
root@galileo:~# dmesg > tester.txt root@galileo:~# ls -las tester.txt 32 -rw-r--r-- 1 root root 32300 Jan 1 2001 tester.txt
#### With DMA on @ 926100 32k file ####
root@galileo:~# echo 0 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# stty -F /dev/ttyS0 921600 root@galileo:~# time cat tester.txt > /dev/ttyS0
real 0m0.421s user 0m0.010s sys 0m0.000s
### With NoDMA on @ 926100 32k file ####
root@galileo:~# echo 3 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# stty -F /dev/ttyS0 921600 root@galileo:~# time cat tester.txt > /dev/ttyS0
real 0m0.421s user 0m0.020s sys 0m0.000s
#### With DMA on @ 9600 32k file #### root@galileo:~# echo 0 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# stty -F /dev/ttyS0 9600 root@galileo:~# time cat tester.txt > /dev/ttyS0
real 0m34.381s user 0m0.000s sys 0m0.010s
#### With NoDMA on @ 9600 32k file ##### root@galileo:~# echo 3 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# stty -F /dev/ttyS0 9600 root@galileo:~# time cat tester.txt > /dev/ttyS0
real 0m34.391s user 0m0.010s sys 0m0.000s
root@galileo:~# ls -las tester_small.txt 4 -rw-r--r-- 1 root root 128 Jan 1 00:06 tester_small.txt
### With DMA on @ 921600 128 byte test file ### root@galileo:~# stty -F /dev/ttyS0 921600 root@galileo:~# echo 0 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# time cat tester_small.txt > /dev/ttyS0
real 0m0.031s user 0m0.010s sys 0m0.000s
### With NoDMA on @ 921600 128 byte test file ### root@galileo:~# stty -F /dev/ttyS0 921600 root@galileo:~# echo 3 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# time cat tester_small.txt > /dev/ttyS0
real 0m0.013s user 0m0.010s sys 0m0.000s
### With DMA on @ 9600 128 byte test file ### root@galileo:~# stty -F /dev/ttyS0 9600 root@galileo:~# echo 0 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# time cat tester_small.txt > /dev/ttyS0
real 0m0.161s user 0m0.000s sys 0m0.010s
### With NoDMA on @ 9600 128 byte test file ### root@galileo:~# stty -F /dev/ttyS0 9600 root@galileo:~# echo 3 > /sys/class/tty/ttyS0/dma_mode root@galileo:~# time cat tester_small.txt > /dev/ttyS0
real 0m0.161s user 0m0.000s sys 0m0.000s
--- bod
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