From: Catalin Marinas <[EMAIL PROTECTED]> Date: Mon, 01 Aug 2005 13:24:04 +0100
> "David S. Miller" <[EMAIL PROTECTED]> wrote: > > If not, you cannot use the lazy dcache flushing method, and in fact > > you must broadcast the flush on all processors. > > Why wouldn't the lazy dcache flushing method work? My understanding is > that if there is no user mapping for a given page, there's no reason > to flush the dcache and just postpone it until the page is faulted > in. When the page fault occurs the dcache should be flushed (on one > CPU is enough) and the icache invalidated on all the CPUs. The "lazy dcache flushing" he mentioned only flushes on the processor where the store occurred, not on any other cpus. He took the sparc64 code which, at the time of the flush_dcache_page() call, stores the current cpu number in the page->flags and sets a bit indicating a flush is needed. When some condition occurs requiring the delayed flush to occur, we look at the cpu number in the page and ask that specific cpu to do the flush. This works perfectly for what sparc64 is trying to do, which is deal with bad aliasing in a virtually indexed D-cache where only the cpu who does the store has to do any flushing, but that won't work for this ARM SMP case at all. I've seen implementations where the I-cache does not snoop local cpu stores, but I've never seen one where other cpus do not snoop such stores. You _HAVE_ to implement handling of I-cache update on L2 cache line changes to handle updates from devices doing DMA, so why in the world special case stores done by other cpus? It almost sounds impossible to implement this and have the I-cache be coherent wrt. DMA transactions. Do you have to flush the whole I-cache every time some device DMAs a page into memory, before you can execute instructions out of it? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
