On Tue, May 15, 2018 at 5:11 PM, Faiz Abbas <faiz_abbas@xxxxxx> wrote: > On Tuesday 15 May 2018 06:09 PM, Linus Walleij wrote: >> On Mon, May 14, 2018 at 1:30 PM, Faiz Abbas <faiz_abbas@xxxxxx> wrote: >> >>> Also, I see many times the number of interrupts for mmc1 in 4.14. >> (...) >>> I also printed out the size of the DMA transfers in the omap_hsmmc >>> driver during the dd command. I see that the maximum size of the dma >>> transfer has decreased from 1 MB to 256kB between 4.13 and 4.14. >> >> This seems like my fault for removing the bounce buffer. >> (The name bounce buffer is misleading, I suspect the right >> term for what is was doing was "merge buffer" or something, >> coalescing physically consecutive requests.) >> >> commit de3ee99b097dd51938276e3af388cd4ad0f2750a >> "mmc: Delete bounce buffer handling" >> should be the culprit. > > I don't think so. I checked out to the commit before that and see that > the interrupts are still too high. OK phew then I'm safe :) >> The bounce buffer only makes any performance impact if the >> host DMA controller is unable to handle scatter-gather lists >> so the number of segments is set down to 1. >> >> Can you verifty that: >> - mmc->max_segs == 1 > > No. It is 64 in v4.14. It was 1024 in v4.13. This smells like: commit 9442400486a1ec28915e9ab31517a5665ed35705 "mmc: omap_hsmmc: Reduce max_segs for reliability" Can you test reverting that and notify Will Newton if this commit is causing performance regressions. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
