mmc: core: complete/wait_for_completion performance

Hi J?rg,

J?rg Krause [off-list ref] hat am 15. Januar 2017 um 21:42 geschrieben:


Hi Stefan,

On Tue, 2016-12-27 at 00:03 +0100, Stefan Wahren wrote:

quoted

Hi J?rg,
...
I also rebased an old patch from Shawn Guo [2] with pre_req and
post_req support, tried to call the DMA channel callback from the
interrupt context instead of scheduling the tasklet within the DMA
engine driver and implement CMD23 support [3]. But none of them show
any measurable performance improvement.

I tested the three patches after disabling any debugging options in the
config. There is no performance gain, but the timings have changed.
Please have a look at the attached graphs. The time between complete()
and wait_for_completion() is reduced to 15us whereas the time from
return from wait_for_completion() to return to sdio_readsb() increases
to 23us (from maybe 2us before).

that confirms my results. I think you are searching on the wrong layer. You better step "back" and take a look at the whole transfer instead of single blocks. Maybe there are some bigger delays.

Stefan

J?rg