On Mon, Sep 17, 2018 at 7:29 AM Heiner Litz <hlitz@xxxxxxxx> wrote: > > Hi All, > this patchset introduces RAIL, a mechanism to enforce low tail read latency for > lightnvm OCSSD devices. RAIL leverages redundancy to guarantee that reads are > always served from LUNs that do not serve a high latency operation such as a > write or erase. This avoids that reads become serialized behind these operations > reducing tail latency by ~10x. In particular, in the absence of ECC read errors, > it provides 99.99 percentile read latencies of below 500us. RAIL introduces > capacity overheads (7%-25%) due to RAID-5 like striping (providing fault > tolerance) and reduces the maximum write bandwidth to 110K IOPS on CNEX SSD. > > This patch is based on pblk/core and requires two additional patches from Javier > to be applicable (let me know if you want me to rebase): As the patches do not apply, could you make a branch available so I can get hold of the code in it's present state? That would make reviewing and testing so much easier. I have some concerns regarding recovery and write error handling, but I have not found anything that can't be fixed. I also believe that rail/on off and stride width should not be configured at build-time, but instead be part of the create IOCTL. See my comments on the individual patches for details. > > The 1st patch exposes some existing APIs so they can be used by RAIL > The 2nd patch introduces a configurable sector mapping function > The 3rd patch refactors the write path so the end_io_fn can be specified when > setting up the request > The 4th patch adds a new submit io function that acquires the write semaphore > The 5th patch introduces the RAIL feature and its API > The 6th patch integrates RAIL into pblk's read and write path > >
