[dm-devel] [PATCH v3 02/14] dm: add ->copy_from_iter() dax operation support
Kani, Toshimitsu
toshi.kani at hpe.com
Thu Jun 15 00:46:14 UTC 2017
On Fri, 2017-06-09 at 13:23 -0700, Dan Williams wrote:
> Allow device-mapper to route copy_from_iter operations to the
> per-target implementation. In order for the device stacking to work
> we
> need a dax_dev and a pgoff relative to that device. This gives each
> layer of the stack the information it needs to look up the operation
> pointer for the next level.
>
> This conceptually allows for an array of mixed device drivers with
> varying copy_from_iter implementations.
>
> Cc: Toshi Kani <toshi.kani at hpe.com>
> Reviewed-by: Mike Snitzer <snitzer at redhat.com>
> Signed-off-by: Dan Williams <dan.j.williams at intel.com>
I was worried about possible overhead with additional stub calls, but
it looks fine with a single thread fio write test with direct=1.
92.62% [kernel.kallsyms] [k] __copy_user_nocache
0.04% [kernel.kallsyms] [k] entry_SYSCALL_64_fastpath
0.08% libpthread-2.22.so [.] __GI___libc_write
0.01% [kernel.kallsyms] [k] sys_write
0.02% [kernel.kallsyms] [k] vfs_write
0.02% [kernel.kallsyms] [k] __vfs_write
0.02% [kernel.kallsyms] [k] ext4_file_write_iter
0.02% [kernel.kallsyms] [k] dax_iomap_rw
0.03% [kernel.kallsyms] [k] iomap_apply
0.04% [kernel.kallsyms] [k] dax_iomap_actor
0.01% [kernel.kallsyms] [k] dax_copy_from_iter
0.01% [kernel.kallsyms] [k] dm_dax_copy_from_iter
0.01% [kernel.kallsyms] [k] linear_dax_copy_from_iter
0.03% [kernel.kallsyms] [k] copy_from_iter_flushcache
0.00% [kernel.kallsyms] [k] pmem_copy_from_iter
Multi-thread fio test hits hard in inode_lock(), no contention from the
dm-layer.
Reviewed-by: Toshi Kani <toshi.kani at hpe.com>
Thanks,
-Toshi
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