Hi, On Wednesday 16 May 2018 07:59 PM, Linus Walleij wrote: > 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" > Yes. I was able to bisect the number of interrupts to the same commit as well. On top of v4.14, *Without revert*: https://pastebin.ubuntu.com/p/VJgvzrCP9g/ avg speed for 100 MB transfer: 3.7 MBps Number of interrupts per 100 MB transfer: ~2000 *After revert*: https://pastebin.ubuntu.com/p/ktgTmKVKkN/ avg speed for 100 MB transfer: 4.6 MBps Number of interrupts per 100 MB transfer: ~500 Also, I'm getting 1M buffers in the omap_hsmmc DMA now. @Will will it be OK to change the mmc_segs back to 1024? Thanks, Faiz -- 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
