Messages in this thread | | | Date | Wed, 28 Nov 2012 17:10:47 -0500 (EST) | From | Mikulas Patocka <> | Subject | Re: [PATCH] Introduce a method to catch mmap_region (was: Recent kernel "mount" slow) |
| |
On Wed, 28 Nov 2012, Linus Torvalds wrote:
> On Wed, Nov 28, 2012 at 12:32 PM, Linus Torvalds > <torvalds@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
| |