27.08.2020 09:45, Adrian Hunter пишет: > 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? That is about 20%. >> 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. > I'll try to take a look at pre/post_req(), but I'm not very familiar with the MMC code, so it may take quite some time. Will be great if you could help with making a patch that I could test!
