On Mon, Feb 10, 2020 at 02:20:10PM -0500, Tim Walker wrote: > Background: > > NVMe specification has hardened over the decade and now NVMe devices > are well integrated into our customers’ systems. As we look forward, > moving HDDs to the NVMe command set eliminates the SAS IOC and driver > stack, consolidating on a single access method for rotational and > static storage technologies. PCIe-NVMe offers near-SATA interface > costs, features and performance suitable for high-cap HDDs, and > optimal interoperability for storage automation, tiering, and > management. We will share some early conceptual results and proposed > salient design goals and challenges surrounding an NVMe HDD. HDD. performance is very sensitive to IO order. Could you provide some background info about NVMe HDD? Such as: - number of hw queues - hw queue depth - will NVMe sort/merge IO among all SQs or not? > > > Discussion Proposal: > > We’d like to share our views and solicit input on: > > -What Linux storage stack assumptions do we need to be aware of as we > develop these devices with drastically different performance > characteristics than traditional NAND? For example, what schedular or > device driver level changes will be needed to integrate NVMe HDDs? IO merge is often important for HDD. IO merge is usually triggered when .queue_rq() returns STS_RESOURCE, so far this condition won't be triggered for NVMe SSD. Also blk-mq kills BDI queue congestion and ioc batching, and causes writeback performance regression[1][2]. What I am thinking is that if we need to switch to use independent IO path for handling SSD and HDD. IO, given the two mediums are so different from performance viewpoint. [1] https://lore.kernel.org/linux-scsi/Pine.LNX.4.44L0.1909181213141.1507-100000@xxxxxxxxxxxxxxxxxxxx/ [2] https://lore.kernel.org/linux-scsi/20191226083706.GA17974@ming.t460p/ Thanks, Ming
