On 27/08/20 9:07 am, Dmitry Osipenko wrote: > Hello! > > I was debugging WiFi performance problems on Acer A500 tablet device > that has BCM4329 WiFi chip which is connected to NVIDIA Terga20 SoC via > SDIO and found that the following commit causes a solid 5-10 Mbit/s of > WiFi throughput regression after 5.2 kernel: What is that in percentage terms? > > commit c07a48c2651965e84d35cf193dfc0e5f7892d612 > Author: Adrian Hunter <adrian.hunter@xxxxxxxxx> > Date: Fri Apr 5 15:40:20 2019 +0300 > > mmc: sdhci: Remove finish_tasklet > > Remove finish_tasklet. Requests that require DMA-unmapping or > sdhci_reset > are completed either in the IRQ thread or a workqueue if the > completion is > not initiated by the IRQ. > > Reverting the offending commit on top of recent linux-next resolves the > problem. > > Ulf / Adrian, do you have any ideas what could be done in regards to > restoring the SDIO performance? Should we just revert the offending commit? > Unfortunately I think we are past the point of returning to the tasklet. sdhci can complete requests in the irq handler but only if ->pre_req() and ->post_req() are used, which is not supported by SDIO at present. pre_req and post_req were introduced to reduce latency for the block driver, so it seems reasonable perhaps to look at using them in SDIO as well.
