On 2016-03-31 22:04, Mike Snitzer wrote:
The primary motivation of this commit is to improve the scalability of
DM multipath on large NUMA systems where m->lock spinlock contention
has
been proven to be a serious bottleneck on really fast storage.
The ability to atomically read a pointer, using lockless_dereference(),
is leveraged in this commit. But all pointer writes are still
protected
by the m->lock spinlock (which is fine since these all now occur in the
slow-path).
The following functions no longer require the m->lock spinlock in their
fast-path: multipath_busy(), __multipath_map(), and do_end_io()
And choose_pgpath() is modified to _not_ update m->current_pgpath
unless
it also switches the path-group. This is done to avoid needing to take
the m->lock everytime __multipath_map() calls choose_pgpath().
But m->current_pgpath will be reset if it is failed via fail_path().
Suggested-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
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