Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 4 Jan 2012 15:10:22 -0800 | Subject | Re: [GIT PULL] slab fixes for 3.2-rc4 |
| |
On Wed, Jan 4, 2012 at 9:00 AM, Christoph Lameter <cl@linux.com> wrote: > > xadd is 3 cycles. add is one cycle.
On some uarchs. On new uarchs it can be a single cycle, I think, and on some uarchs it will even be microcoded and/or only go in one pipe because it has that odd behavior that it writes both to memory and a register, and thus doesn't fit the normal fastpaths.
The point is, xadd isn't actually any faster than just doing the regular "add and read". It's *slower*.
There really isn't ever any reason to use xadd on percpu variables. That's my point. You claimed that there was a performance advantage. There really isn't.
So why are you still arguing?
Linus
| |