On 17 August 2012 09:36, Kent Overstreet <[email protected]> wrote: > On Thu, Aug 16, 2012 at 10:07:29PM +1000, Joseph Glanville wrote: >> There also seems to have been pretty severe performance regressions in >> cache bypassed sequential I/O. >> The newer code barely does 70mb/s sequential writes when >> sequential_cuttoff is set to 4M however it does around 300mb/s when >> set to 0 (no bypass) with dd and 1M block size. >> When using the older codebase the cache bypass is actually slightly >> faster than going to cache at around 360mb/s but this is still much >> slower than the underlying block devices (as previously discussed). > > Ouch. Can you try profiling it with perf while running dd? > > perf record -afg dd etc. etc. > perf report > > should do it
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