On Fri, 27 Jul 2018 14:15:09 -0700 Saeed Mahameed <sae...@mellanox.com> wrote:
> From: Gal Pressman <g...@mellanox.com> > > The VXLAN database is mainly used by readers in data path, and rarely > used by control path writers. > Multiple readers (threads) should not block each other and cause an > unnecessary contention on the lock. > > Replacing the spinlock with rwlock optimizes the common use case where > adding ports to the table (adding VXLAN interfaces) is quite rare, but > the table is accessed for each VXLAN TX skb. > > Signed-off-by: Gal Pressman <g...@mellanox.com> > Signed-off-by: Saeed Mahameed <sae...@mellanox.com> Did you know that for small sections a spinlock is significantly faster than a reader-writer lock. It turns out that reader-writer locks the reader creates a cache line bounce. https://www.kernel.org/doc/Documentation/locking/spinlocks.txt Lesson 2: reader-writer spinlocks. If your data accesses have a very natural pattern where you usually tend to mostly read from the shared variables, the reader-writer locks (rw_lock) versions of the spinlocks are sometimes useful. They allow multiple readers to be in the same critical region at once, but if somebody wants to change the variables it has to get an exclusive write lock. NOTE! reader-writer locks require more atomic memory operations than simple spinlocks. Unless the reader critical section is long, you are better off just using spinlocks.
