Hi Kim, On Wed, Aug 23, 2017 at 11:05:28AM -0500, Kim Phillips wrote: > On Wed, 23 Aug 2017 15:23:18 +0800 > Leo Yan <leo.yan@xxxxxxxxxx> wrote: > > > Cc: Kim Phillips <kim.phillips@xxxxxxx> > > Reported-by: Kim Phillips <kim.phillips@xxxxxxx> > > Thanks; typically only the latter is needed. > > > Set latency request to /dev/cpu_dma_latency to disable all CPUs specific idle > > -states (if latency = 0uS then disable all idle states): > > -# echo "what_ever_latency_you_need_in_uS" > /dev/cpu_dma_latency > > +states (if latency = 0uS then CPU Idle governor selects idle state0, so this > > +means 'WFI' is still enabled but other deeper states have be disabled, this > > +can avoid power off CPUs): > > +# exec 3<> /dev/cpu_dma_latency; echo "what_ever_latency_you_need_in_uS" >&3 > > not a fan of the "what_ever_latency_you_need_in_uS" (including and > especially the quotes which can create ambiguity in the user's mind): > just put a cut-n-pasteable example, clarifying the typically-default > value you chose, and its unit, in the text. > > More to the point, how did you test this? Are you sure that that the > value being echoed isn't being interpreted as a binary number? I checked for this with manually adding log in kernel function, if we use 'echo' command and input string with 4 chars length then the parameter cannot be parsed correctly by copy_from_user(); if input string with other length, the string will be parsed with hexadecimal format. > kernel/power/qos.c:pm_qos_power_read() looks to be looking for a 32-bit > binary integer, but I'm not sure if that's where it gets read. > > Certainly, this 2013 article uses a C example to write a binary integer: > > https://access.redhat.com/articles/65410 > > Please double-check, thanks, Thanks for the reminding. C code with 's32' type can pass correct value into kernel. Have sent new version patch, please help review. Thanks, Leo Yan -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
