On Tue, 2 Feb 2010, Oliver Neukum wrote: > Am Dienstag, 2. Februar 2010 13:39:35 schrieb Catalin Marinas: > > > For storage that is correct. But what about other sources of pages, > > > for example iSCSI? > > > > In the iSCSI case, does the HCD driver write directly to a page cache > > page? Or it just fills in network packets that are copied to page cache > > pages by the iSCSI code (sorry, I'm not familiar with this part of the > > kernel). If the latter, the cache flushing in the HCD driver would not > > help and it needs to be done in the iSCSI code. > > As far as I can tell iSCSI does a private copy. But I don't know how > many methods to transfer code pages over USB exist. I'd say the > conservative solution is to flush for everything but control transfers. This doesn't make any sense. Nobody would ever use isochronous transfers to store data into a code page because isochronous is unreliable. (Audio isn't a counterexample -- audio data may be mapped to userspace, but only to data pages, not code pages. And the problem here is to maintain consistency between the D and I caches.) In principle interrupt transfers could be used, but it is most unlikely. They are intended for bounded-latency transfers, not transfers of potentially large amounts of data. The only transfer type that makes sense to worry about is bulk. Alan Stern -- 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
