Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1251714

Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz

Show all headers | View raw

Hi Guenter,

Quoting Guenter Roeck (2015-10-20 06:30:03)
> On 10/20/2015 06:17 AM, Marc Titinger wrote:
> > On 20/10/2015 14:54, Guenter Roeck wrote:
> >> 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.
> >
> > Re-setting the register address with each read transaction will not prevent another master to change the configuration in your back, in this case. That sounds like a general issue of concurrent clients for one device, this is beyond just reading one register IMO.
> >
> That is an invasive change, though, not just a simple read. Sure, it is
> a risk as well. But it is a different level of risk than someone using
> i2cget or i2cdump while the driver is running.
> 
> >>
> >>> 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.
> > Agreed.
> >
> >>
> >> If you want to convert the driver to regmap, just look for 'regmap' in
> >> drivers/hwmon for examples.
> >
> > Fair enough, but based on your comments, I may look into an iio driver instead for this device, given our application, rather than 'twisting' the hwmon interface.
> >
> 
> Sorry, you lost me there. How are you twisting the hwmon interface ?
> Because I am concerned about multiple accesses from multiple sources ?
> How is iio going to solve that problem ? By ignoring it ?

There is no twisting going on here :-)

We're going to investigate IIO with or without the multi-client/regmap
issues raised in this thread. The purpose is to investigate if we can
get better performance/higher sample rate for our application (the ACME
power measurement device).

> 
> Not that I mind if you want to convert the driver to iio. One less driver
> to take care of. Just asking.

Yup, it's orthogonal to the issues raised here.

Regards,
Mike

> 
> Thanks,
> Guenter
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[RFC] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-19 18:30 +0200
  Re: [RFC] hwmon: ina2xx: allow for actual measurement bandwidth above  160 Hz Guenter Roeck <linux@roeck-us.net> - 2015-10-20 03:40 +0200
    Re: [RFC] hwmon: ina2xx: allow for actual measurement bandwidth above  160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-20 10:00 +0200
    [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-20 10:30 +0200
      Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Guenter Roeck <linux@roeck-us.net> - 2015-10-20 15:00 +0200
        Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-20 15:20 +0200
          Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Guenter Roeck <linux@roeck-us.net> - 2015-10-20 15:40 +0200
            Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-20 15:50 +0200
              Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Guenter Roeck <linux@roeck-us.net> - 2015-10-20 19:10 +0200
                Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth  above 160 Hz Marc Titinger <mtitinger@baylibre.com> - 2015-10-21 09:50 +0200
            Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth above  160 Hz Michael Turquette <mturquette@baylibre.com> - 2015-10-20 16:00 +0200
        [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. Marc Titinger <mtitinger@baylibre.com> - 2015-10-23 18:20 +0200
          Re: [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. Guenter Roeck <linux@roeck-us.net> - 2015-10-23 19:00 +0200
            Re: [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. Marc Titinger <mtitinger@baylibre.com> - 2015-10-23 22:40 +0200
              Re: [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. Guenter Roeck <linux@roeck-us.net> - 2015-10-24 04:30 +0200
              Re: [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. Guenter Roeck <linux@roeck-us.net> - 2015-10-24 14:50 +0200
                [PATCH 0/2] hwmon: ina2xx: convert driver to using regmap Marc Titinger <mtitinger@baylibre.com> - 2015-10-26 17:30 +0100
                [PATCH 2/2] hwmon: ina2xx: give precedence to DT over checking for platform data. Marc Titinger <mtitinger@baylibre.com> - 2015-10-26 17:30 +0100
                Re: [PATCH 2/2] hwmon: ina2xx: give precedence to DT over checking  for platform data. Guenter Roeck <linux@roeck-us.net> - 2015-10-27 02:20 +0100
                [PATCH 1/2] hwmon: ina2xx: convert driver to using regmap Marc Titinger <mtitinger@baylibre.com> - 2015-10-26 17:30 +0100
                Re: [PATCH 1/2] hwmon: ina2xx: convert driver to using regmap Guenter Roeck <linux@roeck-us.net> - 2015-10-27 02:10 +0100
                Re: [PATCH 1/2] hwmon: ina2xx: convert driver to using regmap Guenter Roeck <linux@roeck-us.net> - 2015-10-27 02:20 +0100
                [PATCH v2 1/2] hwmon: ina2xx: convert driver to using regmap Marc Titinger <mtitinger@baylibre.com> - 2015-10-27 11:00 +0100
                [PATCH v2 2/2] hwmon: ina2xx: give precedence to DT over checking for platform data. Marc Titinger <mtitinger@baylibre.com> - 2015-10-27 11:00 +0100
                Re: [PATCH v2 1/2] hwmon: ina2xx: convert driver to using regmap Guenter Roeck <linux@roeck-us.net> - 2015-10-28 03:50 +0100
                Re: [PATCH v2 1/2] hwmon: ina2xx: convert driver to using regmap Marc Titinger <mtitinger@baylibre.com> - 2015-10-28 10:30 +0100
          Re: [RFC] hwmon: ina2xx: port to using remap, improve bandwidth. kbuild test robot <lkp@intel.com> - 2015-10-23 19:00 +0200

csiph-web