Messages in this thread | | | Date | Mon, 22 Jun 1998 07:27:47 -0400 | From | "Alex P. Madarasz, Jr." <> | Subject | Re: RT cache management |
| |
At 6/22/98 04:18 AM , Rik van Riel wrote: > On Sun, 21 Jun 1998, Jeff Millar wrote: > > Recalling the questions: What cache control features do RTOS's have that > > Linux doesn't? Does Linux have another approach to achieve the benefits of > > cache control? Do applications really need cache control? > > Linux has some cache controlling features, but they're not > application program tunable. All Linux machines are > automatically cache coherent, so programs don't really need > that kind of control anyway... > > If memory is shared, you probably want to pay the price > for cache coherency, if memory is not shared, you're not > paying the price anyway...
I believe the original poster was discussing multi-processor "shared memory" (also called "reflected" memory) hardware systems, where the shared memory (usually on a peripheral card for PCs) is multi-ported via a high-speed serial/parallel bus and has a "back-door" port from one system to another which is not controlled / controllable by the mobo chipset. See, for example, Systran's SCRAMnet series at :
<http://www.systran.com/scramnet.htm>
In such a system, the mobo chipset memory controller isn't integrated with the shared memory, and a remote system can write to a local shared memory location without the local system's chipset / CPU being notified, invalidating the local / CPU cache without notifying the local system of the fact. In RTOSs which allow for such a setup, you can tell the OS that a block of memory is to be locked down (not pageable) and not cached, so that the CPU / chipset is always forced to fetch data directly from the shared memory rather than from cache.
--------------------------------------------- Alex P. Madarasz, Jr. -- madarasz@erols.com
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu
| |