On 2007-Feb-20 02:47:00 -0500, Zaphod Beeblebrox <[EMAIL PROTECTED]> wrote: >On 2/17/07, Peter Jeremy <[EMAIL PROTECTED]> wrote: >>I've tried modelling a unified cache along the NetBSD line and there >>appears to be a massive improvement in cache performance. It's unclear >>how much of an improvement this will give in overall performance but >>not physically reading data from disk must be faster than reading it. > >This squares perfectly with my recent observation that while runing some >combination of "dump | restore" that the dump disks incur 2 to 3 times more >I/O (reading) than the restore disks. Now... for "performance" I was using >the cache function --- maybe the cache is actually a detriment.
The limited testing I've done suggests that 32MB cache gives you a 10-20% improvement in dump speed. This would heavily dependent on the disk I/O performance - a slow CPU running PIO might be better off without caching. I've found that you do get a worthwhile improvement in dump|restore performance by introducing a large (10's of MB) fifo between them. This helps reduce synchronisation between dump and restore (so that dump can continue to read whilst restore is busy writing a batch of small files and vice versa). There's a suitable port but I can't recall the name because I wrote my own. >>I believe it would be worthwhile creating a todo item to investigate >>this more thoroughly. Note that I think that fixing this is a weekend job, rather than a SoC project. -- Peter Jeremy
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