From: Guenter Roeck <linux@roeck-us.net>
To: Marc Titinger <mtitinger@baylibre.com>, jdelvare@suse.com
Cc: lm-sensors@lm-sensors.org, linux-kernel@vger.kernel.org,
bcousson@baylibre.com, mturquette@baylibre.com
Subject: Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz
Date: Tue, 20 Oct 2015 05:54:11 -0700 [thread overview]
Message-ID: <56263973.300@roeck-us.net> (raw)
In-Reply-To: <1445329244-21627-1-git-send-email-mtitinger@baylibre.com>
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
next prev parent reply other threads:[~2015-10-20 12:54 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-19 16:21 [RFC] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz Marc Titinger
2015-10-20 1:32 ` Guenter Roeck
2015-10-20 7:58 ` Marc Titinger
2015-10-20 8:20 ` [PATCH v2] " Marc Titinger
2015-10-20 12:54 ` Guenter Roeck [this message]
2015-10-20 13:17 ` Marc Titinger
2015-10-20 13:30 ` Guenter Roeck
2015-10-20 13:46 ` Marc Titinger
2015-10-20 17:00 ` Guenter Roeck
2015-10-21 7:46 ` Marc Titinger
2015-10-20 13:52 ` Michael Turquette
2015-10-23 16:13 ` [RFC] hwmon: ina2xx: port to using remap, improve bandwidth Marc Titinger
2015-10-23 16:49 ` kbuild test robot
2015-10-23 16:52 ` Guenter Roeck
2015-10-23 20:35 ` Marc Titinger
2015-10-24 2:21 ` Guenter Roeck
2015-10-24 12:45 ` Guenter Roeck
2015-10-26 16:24 ` [PATCH 0/2] hwmon: ina2xx: convert driver to using regmap Marc Titinger
2015-10-26 16:24 ` [PATCH 1/2] " Marc Titinger
2015-10-27 1:02 ` Guenter Roeck
2015-10-27 1:12 ` Guenter Roeck
2015-10-27 9:51 ` [PATCH v2 " Marc Titinger
2015-10-28 2:47 ` Guenter Roeck
2015-10-28 9:23 ` Marc Titinger
2015-10-26 16:24 ` [PATCH 2/2] hwmon: ina2xx: give precedence to DT over checking for platform data Marc Titinger
2015-10-27 1:10 ` Guenter Roeck
2015-10-27 9:51 ` [PATCH v2 " Marc Titinger
2015-10-23 16:55 ` [RFC] hwmon: ina2xx: port to using remap, improve bandwidth kbuild test robot
2015-10-23 20:10 ` kbuild test robot
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