On 10/20/2015 01:20 AM, Marc Titinger wrote:
With the current implementation, the driver will prevent a readout at a pace faster than the default conversion time (2ms) times the averaging setting, min AVG being 1:1. Any sysfs "show" read access from the client app faster than 500 Hz will be 'cached' by the driver, but actually since do_update reads all 8 registers, the best achievable measurement rate is roughly 8*800 us (for the time spent in i2c-core) i.e. <= 156Hz with Beagle Bone Black. This change set uses a register mask to allow for the readout of a single i2c register at a time. Furthermore, performing subsequent reads on the same register will make use of the ability of the i2c chip to retain the last reg offset, hence use a shorter i2c message (roughly 400us instead of 800us spent in i2c-core.c).
That doesn't work. There could be accesses from other sources (such as through i2c-dev, or in multi-master systems) between two reads.
The best readout rate for a single measurement is now around 2kHz. And for four measurements around (1/(4*800us) = 312 Hz. Since for any readout rate faster than 160 Hz the interval is set by the i2c transactions completion, the 'last-update' anti-flooding code will not have a limiting effect in practice. Hence I also remove the elapsed time checking in the hwmon driver for ina2xx. To summarize, the patch provides a max bandwidth improvement with hwmon client apps from ~160 Hz to ~320 Hz, and better in single-channel polling mode.
Overall your patch pretty much re-implements regmap. Since you drop caching, it is also unnecessary to read all registers at a time, so you can just use a function to read _one_ register and returns its value (with retries). Or use regmap. Either case, do_update() and ina2xx_update_device() are no longer needed. If you want to convert the driver to regmap, just look for 'regmap' in drivers/hwmon for examples. Guenter _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
