Hi
On 04/01/2016 05:47 AM, Lucas De Marchi wrote:
From: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Disabling the adapter after each transfer is pretty bad for sensors and
other devices doing small transfers at a high rate. It slows down the
transfer rate a lot since each of them have to wait the adapter to be
enabled again.
It was done in order to avoid the adapter to generate interrupts when
it's not being used. Instead of doing that here we just disable the
interrupt generation in the controller. With a small program test to
read/write registers in a sensor the speed doubled. Example below with
write sequences of 16 bytes:
Before:
i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07
num_transfers=20000
transfer_time_avg=1032.728500us
After:
i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07
num_transfers=20000
transfer_time_avg=470.256050us
I gave a test to this patch and saw similar improvements when dumping
large set of registers from I2C connected audio codec.
echo Y > /sys/kernel/debug/regmap/i2c-10EC5640\:00/cache_bypass
time cat /sys/kernel/debug/regmap/i2c-10EC5640\:00/registers >/dev/null
I checked the runtime PM status of adapter was suspended before running
above cat command in order to get comparable results.
Before patch time was ~0.55 - ~0.76 s and with patch applied time was
~0.16 - ~0.25 s.
Hopefully we'll find how to prevent regression on Christian's machines.
--
Jarkko
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