On Wed, 28 Nov 2012, Linus Torvalds wrote:
> On Wed, Nov 28, 2012 at 12:32 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: > > > > Here is a *COMPLETELY* untested patch. Caveat emptor. It will probably > > do unspeakable things to your family and pets. > > Btw, *if* this approach works, I suspect we could just switch the > bd_block_size_semaphore semaphore to be a regular rw-sem. > > Why? Because now it's no longer ever gotten in the cached IO paths, we > only get it when we're doing much more expensive things (ie actual IO, > and buffer head allocations etc etc). As long as we just work with the > page cache, we never get to the whole lock at all. > > Which means that the whole percpu-optimized thing is likely no longer > all that relevant. Using normal semaphore degrades direct-IO performance on raw devices, I measured that (45.1s with normal rw-semaphore vs. 42.8s with percpu-rw-semaphore). It could be measured on ramdisk or high-performance SSDs. Mikulas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
