On Tue, Oct 21, 2014 at 12:13:22AM +0300, Or Gerlitz wrote: > On Mon, Oct 20, 2014 at 6:29 PM, Chris Moore <Chris.Moore@xxxxxxxxxx> wrote: > > The following code is in isert_conn_setup_qp() in ib_isert.c: > > > > /* > > * FIXME: Use devattr.max_sge - 2 for max_send_sge as > > * work-around for RDMA_READ.. > > */ > > attr.cap.max_send_sge = device->dev_attr.max_sge - 2; > > > > It's not clear from the comment what this is a work-around for, and I wasn't able > > to figure it out from looking at logs. > > I believe this refers to some IBTA spec corner case which comes into > play with the max_sges advertized by mlx4, Eli, can you shed some > light (IBTA pointer) on that? is this the case (i.e dev_attr.max_sge > isn't always achievable) with mlx5 too? > I don't think it has to do anything with some corner case. If you look at the spec you will find that is not guarnteed that whenever you create a QP with device->dev_attr.max_sge it will succeed. The consumer should try smaller values if it cannot create a QP with max sge. This is from IB spec 1.2.1. 11.2.1.2 QUERY HCA Description: Returns the attributes for the specified HCA. The maximum values defined in this section are guaranteed not-to-exceed values. It is possible for an implementation to allocate some HCA resources from the same space. In that case, the maximum values returned are not guaranteed for all of those resources simultaneously. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
