On Fri, Sep 23, 2016 at 8:05 AM, Thor Lancelot Simon <t...@panix.com> wrote: > Our storage stack's inability to use tags with SATA targets is a huge > gating factor for performance with real workloads (the residual use of > the kernel lock at and below the bufq layer is another).
FreeBSD's storage stack does support NCQ. When that's artificially turned off, performance drops on a certain brand of SSDs from about 500-550MB/s for large reads down to 200-300MB/s depending on too many factors to go into here. It helps a lot for work loads and is critical for Netflix to get 36-38Gbps rate from our 40Gbps systems. > Starting de > novo with NVMe, where it's perverse and structurally difficult to not > support multiple commands in flight simultaneously, will help some, but > SATA SSDs are going to be around for a long time still and it'd be > great if this limitation went away. NVMe is even worse. There's one drive that w/o queueing I can barely get 1GB/s out of. With queueing and multiple requests I can get the spec sheet rated 3.6GB/s. Here queueing is critical for Netflix to get to 90-93Gbps that our 100Gbps boxes can do (though it is but one of many things). > That said, I am not going to fix it myself so all I can do is sit here > and pontificate -- which is worth about what you paid for it, and no > more. Yea, I'm just a FreeBSD guy lurking here. Warner