On Mon, Jun 24, 2019 at 01:24:15PM -0400, Alan Stern wrote: > On Mon, 24 Jun 2019, Suwan Kim wrote: > > > > > + hcd->self.sg_tablesize = ~0; > > > > + hcd->self.no_sg_constraint = 1; > > > > > > You probably shouldn't do this, for two reasons. First, sg_tablesize > > > of the server's HCD may be smaller than ~0. If the client's value is > > > larger than the server's, a transfer could be accepted on the client > > > but then fail on the server because the SG list was too big. > > On the other hand, I don't know of any examples where an HCD has > sg_tablesize set to anything other than 0 or ~0. vhci-hcd might end up > being the only one. > > > > Also, you may want to restrict the size of SG transfers even further, > > > so that you don't have to allocate a tremendous amount of memory all at > > > once on the server. An SG transfer can be quite large. I don't know > > > what a reasonable limit would be -- 16 perhaps? > > > > Is there any reason why you think that 16 is ok? Or Can I set this > > value as the smallest value of all HC? I think that sg_tablesize > > cannot be a variable value because vhci interacts with different > > machines and all machines has different sg_tablesize value. > > I didn't have any good reason for picking 16. Using the smallest value > of all the HCDs seems like a good idea. I also have not seen an HCD with a value other than ~0 or 0 except for whci which uses 2048, but is not 2048 the maximum value of sg_tablesize? If so, ~0 is the minimum value of sg_tablesize that supports SG. Then can vhci use ~0 if we don't consider memory pressure of the server? If all of the HCDs supporting SG have ~0 as sg_tablesize value, I think that whether we use an HCD locally or remotely, the degree of memory pressure is same in both local and remote usage. Regards Suwan Kim
