On Wed, 2013-11-13 at 16:58 +0000, David Laight wrote: [...] > > > > > You can split a bulk TD on a 1k boundary and the target won't know the > > > > > difference. > > > > > > > > The target won't know the difference, but the host will. Here's an > > > > example: Suppose the driver submits two URBs, each for a data-in > > > > transfer of 32 KB. You split each URB up into two 16-KB TDs; let's > > > > call them A, B, C, and D (where A and B make up the first URB, and C > > > > and D make up the second URB). > > > > > > I was thinking about OUT transfers, IN ones are unlikely to be badly > > > fragmented. > > > > Maybe not for the network stack, but OUT and IN end up equally > > fragmented for the storage stack. > > But the minimum fragment size is (probably) 4k. > For the network stack an OUT transfer might have a lot (and I mean lots) > of fragments (there may be constraints, and linearising the skb is a option). [...] The maximum number of fragments in the skb is going to be 17 (including the 'head' area). (I'm ignoring NETIF_F_FRAGLIST which is not normally supported by physical device drivers.) I don't know how many fragments that can end up as, at the USB level. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- 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
