Messages in this thread | | | Date | Tue, 16 Dec 2003 16:54:50 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [CFT][RFC] HT scheduler |
| |
On Tue, 16 Dec 2003, Linus Torvalds wrote:
> On Tue, 16 Dec 2003, Davide Libenzi wrote: > > > I bet it is. In a big way. > > > > > > The lock does two independent things: > > > - it tells the core that it can't just crack up the load and store. > > > - it also tells other memory ops that they can't re-order around it. > > > > You forgot the one where no HT knowledge can be used for optimizations. > > > > - Asserting the CPU's #LOCK pin to take control of the system bus. That in > > MP system translate into the signaling CPU taking full control of the > > system bus until the pin is deasserted. > > I think this is historical and no longer true. > > All modern CPU's do atomic accesses on a cache coherency (and write buffer > ordering) level, and it has nothing to do with the external bus any more. > > I suspect locked accesses to memory-mapped IO _may_ still set an external > flag, but I seriously doubt anybody cares. I wouldn't be surprised if the > pin doesn't even exist any more.
I just checked the P6 stuff. It does exist but it can is some cases (write-back access on data completely on cache, for example) be caught by the cache controller that handles the following ops using normal cache coherency mechanisms.
- Davide
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |