Re: [PATCH v5 00/11] serial: 8250: split LPSS to 8250_lpss, enable DMA on Quark

Andy Shevchenko
2016-05-24T18:07:14Z

On Tue, 2016-05-24 at 20:37 +0300, Andy Shevchenko wrote:
> On Thu, 2016-05-19 at 02:18 +0100, Bryan O'Donoghue wrote:
> > On Thu, 2016-05-12 at 18:06 +0300, Andy Shevchenko wrote:
> > > On Fri, 2016-05-06 at 18:17 +0300, Andy Shevchenko wrote:
> > > > This is combined series of two things:
> > > > - split out the Intel LPSS specific driver from 8250_pci into
> > > > 8250_lpss
> > > > - enable DMA support on Intel Quark UART
> > > >
> > > > The patch has been tested on few Intel SoCs / platforms. In any
> > > > case I
> > > > would
> > > > like to ask Bryan to do independent test.
> >
> > Andy.
> >
> > It looks as though there's a performance drop when enabling the DMA
> > here (v) stock PIO mode with the 8250 driver.

Wait, the time measurement you done is unrelated to DMA/non-DMA mode.
It's significantly depend to the speed of the port.

It would be better to have 1000(s) of iterations to see any steady
difference out of statistical error. Below result doesn't show anything
like this.

I also tried on my Galileo board, I used longer data stream, i.e. output
of dmesg (since your data pattern makes 0:s in statistics) and got
something quite near to each other:

###
Size of the data (it actually become few dozens of bytes (55 bytes to be
precise) bigger since one message had been printed in the second part of
high speed test
###

% dmesg | wc -c
34965

### Low speed, DMA mode enabled by default ###
% stty -F /dev/ttyS0 9600

% time dmesg > /dev/ttyS0
real    0m 34.22s
user    0m 0.01s
sys     0m 0.02s

NOTE: Transfer speed: 34965b/34.22s ~= 1021.77b/s (9600 baud)

### non-DMA mode ###
% echo 3 > /sys/class/tty/ttyS0/dma_mode

% time dmesg > /dev/ttyS0
real    0m 36.09s
user    0m 0.01s
sys     0m 0.02s

### Higher speed ###

% stty -F /dev/ttyS0 921600

% time dmesg > /dev/ttyS0
real    0m 0.41s
user    0m 0.01s
sys     0m 0.03s

NOTE: Transfer speed: 34965b/0.41s ~= 85280.49b/s (921600 baud)

### DMA mode enabled ###
% echo 0 > /sys/class/tty/ttyS0/dma_mode

% time dmesg > /dev/ttyS0
real    0m 0.41s
user    0m 0.01s
sys     0m 0.02s

>
> Below results doesn't show DMA case (by the way, how did you disable
> DMA
> in 3.8.7?) for stock kernel.
>
> Anyway, I added preliminary support to change DMA mode run-time. Check
> my today topic/dw/qrk branch. It would be nice to see all 4 cases: DMA
> vs non-DMA on stock kernel (Yocto) and mine.
>
> P.S. What is the point to test arbitrary tip branch?
>
> >
> > Test setup Galileo Gen1 transmitter - Galileo Gen2 receiver. TX/RX
> > cross-wired between the Arduino UART headers respectively (pins 0 &
> > 1
> > on the "Digital PWM" header), GND pin14 similarly cross-wired.
> >
> > User-space:
> >     Receiver: Stock on-flash yocto-tiny kernel 3.8.7
> >     Transmitter: Galileo Debian image :
> >                  https://sourceforge.net/projects/galileodebian/
> >     3.8.7 kernel: On SPI-flash BSP kernel
> >     andy-v4: From your tree
> >              d13ffcf ('serial: 8250: attempt to keep Kconfig and
> >                        Makefile in order')
> >     tip-of-tree : 97f0090 ('Merge tag 'rproc-v4.7' of
> >                             git://github.com/andersson/remoteproc')
> >
> > Results:
> >
> > ### Test0 ###
> >
> > galileo dma andy-v4 9600 8n1
> >
> > root@galileo:~# time echo "abcdefghijklmnopqrstuvwxyz0123456789" >
> > /dev/ttyS0
> >
> > real    0m0.060s
> > user    0m0.000s
> > sys     0m0.000s
> >
> >
> > galileo non-dma Linux 3.8.7 9600 8n1:
> >
> > 9600 8n1
> > root@galileo:~# time echo "abcdefghijklmnopqrstuvwxyz0123456789" >
> > /dev/ttyS0
> >
> > real    0m0.051s
> > user    0m0.000s
> > sys     0m0.000s
> >
> > galileo non-dma tip-of-tree 9600 8n1:
> >
> > root@galileo:~# time echo "abcdefghijklmnopqrstuvwxyz0123456789" >
> > /dev/ttyS0
> >
> > real    0m0.048s
> > user    0m0.000s
> > sys     0m0.000s
> >
> >
> > ### Test1 ###
> >
> > galileo dma andy-v4 9600 8n1:
> >
> > root@galileo:~# time echo
> > "abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz01234
> > 56
> > 7
> > 89abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz0123
> > 45
> > 6
> > 789abcdefghijklmnopqrstuvwxyz0123456789" > /dev/ttyS0
> >
> > real    0m0.209s
> > user    0m0.000s
> > sys     0m0.000s
> >
> > galileo non-dma Linux 3.8.7 9600 8n1:
> >
> > root@galileo:~# time echo
> > "abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz01234
> > 56
> > 7
> > 89abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz0123
> > 45
> > 6
> > 789abcdefghijklmnopqrstuvwxyz0123456789" > /dev/ttyS0
> >
> > real    0m0.206s
> > user    0m0.000s
> > sys     0m0.000s
> >
> >
> > galileo non-dma tip-of-tree 9600 8n1:
> >
> > root@galileo:~# time echo
> > "abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz01234
> > 56
> > 7
> > 89abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz0123
> > 45
> > 6
> > 789abcdefghijklmnopqrstuvwxyz0123456789" > /dev/ttyS0
> >
> > real    0m0.199s
> > user    0m0.010s
> > sys     0m0.000s

--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy