[c++] [hwmon] std::ifstream read file with timeout so long

Patrick Williams patrick at stwcx.xyz
Thu Oct 8 02:24:28 AEDT 2020

On Tue, Oct 06, 2020 at 10:42:18PM +0700, Nguyen Chanh wrote:
> In https://github.com/openbmc/phosphor-hwmon => hwmonio.cpp , I saw we use
> the std::ifstream to open and read a device sensor.
> But, I met an issue with it. In case the sensor was disabled (Ex: the Fan
> was unplugged), the std::ifstream read will take a long time . The timeout
> in there is so long. It makes my system have a BIG delay in each checking
> sensor.
> Other observation : In case the sensor device is ready, the time for sensor
> reading is expected.
> Measuring std::ifstream reading:
> In case unplugged sensor: 91385 microseconds
> In case plugged sensor. : 507 microseconds

Do you know which device driver it is interacting with?  This sounds
like an issue with the underlying driver.  Perhaps it is attempting
too many retries.

> The patch to measure the std::ifstream reading, please see attachment !
> Unexpected behavior you saw
> The timeout in there is so long
> Expected behavior
> Do we have any better solution in this case? take less more timeout.
> [image: Screen Shot 2020-10-03 at 11.32.36 AM.png]
> -- 
> *Nguyen Minh Chanh *
> *Embedded Software Engineer *

Patrick Williams
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