Messages in this thread | | | Date | Mon, 27 Jun 2005 16:43:32 +1000 | From | Nick Piggin <> | Subject | VFS scalability (was: [rfc] lockless pagecache) |
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Just an interesting aside, when first testing the patch I was using read(2) instead of nopage faults. I ran into some surprising results there which I don't have the time to follow up at the moment - it might be worth investigating if someone has the time, regardless the state of the lockless pagecache work.
For the parallel workload as described in the parent post (but read instead of fault), the vanilla kernel profile looks like this:
74453 total 0.0121 25839 update_atime 44.8594 19595 _read_unlock_irq 306.1719 13025 do_generic_mapping_read 5.5758 9374 rw_verify_area 29.2937 1739 ia64_pal_call_static 9.0573 1567 default_idle 4.0807 1114 __copy_user 0.4704 848 _spin_lock 8.8333 786 ia64_spinlock_contention 8.1875 246 ia64_save_scratch_fpregs 3.8438 187 ia64_load_scratch_fpregs 2.9219 16 file_read_actor 0.0263 15 fsys_bubble_down 0.0586 12 vfs_read 0.0170
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.
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