On 2013-Mar-03 23:12:40 -0800, Don Lewis <truck...@freebsd.org> wrote: >On 4 Mar, Konstantin Belousov wrote: >> It could be argued that the current typical value of 16MB for the >> hirunningbufspace is too low, but experiments with increasing it did >> not provided any measureable change in the throughput or latency for >> some loads. > >The correct value is probably proportional to the write bandwidth >available.
The problem is that write bandwidth varies widely depending on the workload. For spinning rust, this will vary between maybe 64KBps (512B random writes) and 100-150MBps (single-theaded large sequential writes). The (low-end) SSD in my Netbook also has about 100:1 variance due to erase blocking. How do you tune hirunningbufspace in the face of 2 or 3 orders of magnitude variance in throughput? Especially since SSDs don't gradually degrade - they hit a brick wall. -- Peter Jeremy
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