>>>>> "Tom" == Tom Yan <tom.ty89@xxxxxxxxx> writes: Tom, Tom> Now let's just come back to libata. I've thought of reporting dev-> Tom> max_sectors as Optimal Transfer Length in the SATL. However, I am Tom> not sure if it is a safe thing to do, because we set it as high as Tom> 65535 for devices with LBA48 devices. Does such a high max_sectors Tom> ever make sense in libata's case? I don't agree with conflating the optimal transfer size and the maximum supported ditto. Submitting the largest possible I/O to a device does not guarantee that you get the best overall performance. - max_hw_sectors is gated by controller DMA constraints. - max_dev_sectors is set for devices that explicitly report a transfer length limit. - max_sectors, the soft limit for filesystem read/write requests, should be left at BLK_DEF_MAX_SECTORS unless the device explicitly requests transfers to be aligned multiples of a different value (typically the internal stripe size in large arrays). The point of BLK_DEF_MAX_SECTORS is to offer a reasonable default for common workloads unless otherwise instructed by the storage device. We can have a discussion about what the right value for BLK_DEF_MAX_SECTORS should be. It has gone up over time but it used to be the case that permitting large transfers significantly impacted interactive I/O performance. And finding a sweet spot that works for a wide variety of hardware, interconnects and workloads is obviously non-trivial. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
