On 9/13/06, Jakob Oestergaard <jakob@xxxxxxxxxxxxx> wrote:
On Mon, Sep 11, 2006 at 04:00:32PM -0700, Dan Williams wrote: > Neil, > ... > > Concerning the context switching performance concerns raised at the > previous release, I have observed the following. For the hardware > accelerated case it appears that performance is always better with the > work queue than without since it allows multiple stripes to be operated > on simultaneously. I expect the same for an SMP platform, but so far my > testing has been limited to IOPs. For a single-processor > non-accelerated configuration I have not observed performance > degradation with work queue support enabled, but in the Kconfig option > help text I recommend disabling it (CONFIG_MD_RAID456_WORKQUEUE). Out of curiosity; how does accelerated compare to non-accelerated?
One quick example: 4-disk SATA array rebuild on iop321 without acceleration - 'top' reports md0_resync and md0_raid5 dueling for the CPU each at ~50% utilization. With acceleration - 'top' reports md0_resync cpu utilization at ~90% with the rest split between md0_raid5 and md0_raid5_ops. The sync speed reported by /proc/mdstat is ~40% higher in the accelerated case. That being said, array resync is a special case, so your mileage may vary with other applications. I will put together some data from bonnie++, iozone, maybe contest, and post it on SourceForge.
/ jakob
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