Messages in this thread | | | From | Jesse Barnes <> | Subject | Re: Buffered I/O slowness | Date | Mon, 1 Nov 2004 10:26:34 -0800 |
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On Friday, October 29, 2004 5:30 pm, Andrew Morton wrote: > Jesse Barnes <jbarnes@engr.sgi.com> wrote: > > > I'm not sure that we know what's going on yet. I certainly don't. The > > > above numbers look good, so what's the problem??? > > > > The numbers are ~1/3 of what the machine is capable of with direct I/O. > > Are there CPU cycles to spare? If you have just one CPU copying 1GB/sec > out of pagecache, maybe it is pegged?
Hm, I thought I had more CPU to spare, but when I set the readahead to a large value, I'm taking ~100% of the CPU time on the CPU doing the read. ~98% of that is system time. When I run 8 copies (this is an 8 CPU system), I get ~4GB/s and all the CPUs are near fully busy. I guess things aren't as bad as I initially thought.
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