Re: VFS scalability (was: [rfc] lockless pagecache)

[Andi Kleen]

Nick Piggin <nickpiggin@xxxxxxxxxxxx> writes:

> This is with the filesystem mounted as noatime, so I can't work
> out why update_atime is so high on the list. I suspect maybe a
> false sharing issue with some other fields.

Did all the 64CPUs write to the same file?

Then update_atime was just the messenger - it is the first function
to read the inode so it eats the cache miss overhead.

Maybe adding a prefetch for it at the beginning of sys_read() 
might help, but then with 64CPUs writing to parts of the inode
it will always thrash no matter how many prefetches.

-Andi
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