On Mon, Jan 09, 2012 at 11:24:42AM -0500, Alan Stern wrote: > On Mon, 9 Jan 2012, Felipe Balbi wrote: > > > > However, keep in mind that not all HCDs need to support UAS. Unless > > > somebody makes a device with UAS and without BOT, we afford to make UAS > > > unavailable on host controllers without SG support -- expecially if > > > those controllers can't go any faster than full speed anyway. > > > > MUSB can go up to highspeed and it won't support SGs easily. At least > > not with the internal Inventra DMA Engine. > > Okay, so there are some hardware setups that won't go as fast as they > might. The lossage isn't all that great, because even at high speed > UAS isn't that much faster than BOT. > > (Although, I admit, it would be nice to have some benchmark figures to > back up this claim...) When I measured our (I mean Linux's) implementation of UASP and g_mass_storage were behaving quite the same throghput-wise. But then again, device and host were quite powerful machines (quadcore with 16GiB RAM). I guess when CPU(s) is(are) busy, that memcpy which we save when using VFS's SG list will pay off. -- balbi
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