Hello, I'm DMA seeing performance loss related to CONFIG_PM on OMAP3. # CONFIG_PM is set: echo 3 > /proc/sys/vm/drop_caches # file copy from NAND (using NAND driver in DMA mode) dd if=/mnt/tmp/a of=/dev/null bs=1M count=32 33554432 bytes (32.0MB) copied, 9.088714 seconds, 3.5MB/s # file read from SD (hsmmc uses DMA) dd if=/dev/mmcblk0 of=/dev/null bs=1M count=32 33554432 bytes (32.0MB) copied, 2.065460 seconds, 15.5MB/s # CONFIG_PM not set: # NAND dd if=/mnt/tmp/a of=/dev/null bs=1M count=32 33554432 bytes (32.0MB) copied, 5.653534 seconds, 5.7MB/s # SD dd if=/dev/mmcblk0 of=/dev/null bs=1M count=32 33554432 bytes (32.0MB) copied, 1.919007 seconds, 16.7MB/s While SD card performance loss is not that bad (~7%), NAND one is worrying (~39%). I've tried disabling/enabling CONFIG_CPU_IDLE, also cpuidle states over sysfs, it did not have any significant effect. Is there something else to try? I'm guessing this is caused by CPU wakeup latency to service DMA interrupts? I've noticed that if I keep CPU busy, the loss is reduced almost completely. Talking about cpuidle, what's the difference between C1 and C2 states? They look mostly the same. Then there is omap3_do_wfi, it seems to be unconditionally putting SDRC on self-refresh, would it make sense to just do wfi in higher power states, like OMAP4 seems to be doing? -- Gražvydas -- 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
