Messages in this thread | | | Date | Sat, 11 Oct 2008 15:11:15 +0200 | From | Andi Kleen <> | Subject | Re: Update cacheline size on X86_GENERIC |
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> > > That would be nice. It would be interesting to know what is causing > > > the slowdown. > > > > At least that test is extremly cache footprint sensitive. A lot of the > > cache misses are surprisingly in hd_struct, because it runs > > with hundred of disks and each needs hd_struct references in the fast path. > > The recent introduction of fine grained per partition statistics > > caused a large slowdown. But I don't think kernel workloads > > are normally that extremly cache sensitive. > > That's interesting. struct device is pretty big. I wonder if fields
Yes it is (it actually can be easily shrunk -- see willy's recent patch to remove the struct completion from knodes), but that won't help because it will always be larger than a cache line and it's in the middle, so the accesses to first part of it and last part of it will be separate.
> couldn't be rearranged to minimise the fastpath cacheline footprint? > I guess that's already been looked at?
Yes, but not very intensively. So far I was looking for more detailed profiling data to see the exact accesses.
Of course if you have any immediate ideas that could be tried too.
-Andi
-- ak@linux.intel.com
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