On Thu, 2010-03-04 at 21:37 +0000, Benjamin Herrenschmidt wrote: > On Thu, 2010-03-04 at 18:07 +0000, Catalin Marinas wrote: > > I'm not familiar with SH but for PIO devices the flushing shouldn't be > > more aggressive. For the DMA devices, Russell suggested that we mark > > the page as clean (set PG_dcache_clean) in the DMA API to avoid the > > default flushing. > > I really like that idea, as I said earlier, but I'm worried about the I$ > side of things. IE. What I'm trying to say is that I can't see how to do > that optimisation without ending up with missing I$ invalidations or > doing way too many of them, unless we have a separate bit to track I$ > state. But does this optimisation really matter? I think with careful checking in set_pte_at(), you are not going to invalidate the I-cache more than necessary. If the original page wasn't pte_present() you would need to do the I-cache invalidation. The other cases where set_pte_at() is called for LRU (pte_young) or COW (pte_write) we can avoid the extra invalidation. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
