[dpdk-dev] [PATCH v13 2/2] kni: support IOVA mode

[David Marchand]

On Fri, Nov 15, 2019 at 2:40 PM Jerin Jacob <jerinjacobk at gmail.com> wrote:
> On Fri, Nov 15, 2019 at 6:29 PM David Marchand
> <david.marchand at redhat.com> wrote:
> > So far, KNI could not work with IOVA as VA.
> > Your patchset adds support for IOVA as VA if kernel is >= 4.6.
>
> We need achive the following.
>
> IOVA as PA  has performance implication on KNI case. So we need to
> make IOVA as PA when KNI module is loaded.

- The current behaviour is:
  * buses announce PA, nothing to do wrt KNI,
  * buses announce VA or DC (whatever the considerations on iommu), if
physical addresses are available, then PA is used and KNI works,

- Now, with this new feature (on kernels >= 4.6), we can have KNI work
with VA, the previous workaround can be skipped.
There is another consideration wrt performance, as a consequence, for
kernels 4.6, if physical addresses are available, we can select PA for
KNI.

_But_ I did not see people complaining about the current behavior.
I see no reason to change this if the VA support can't be used (kernels < 4.6).

So how about (I inverted the #if LINUX_VERSION_CODE >=
KERNEL_VERSION(4, 6, 0), it was causing me headaches):

diff --git a/lib/librte_eal/linux/eal/eal.c b/lib/librte_eal/linux/eal/eal.c
index 9e2d50cfb..33f3c674c 100644
--- a/lib/librte_eal/linux/eal/eal.c
+++ b/lib/librte_eal/linux/eal/eal.c
@@ -1073,6 +1073,11 @@ rte_eal_init(int argc, char **argv)
                                 */
                                iova_mode = RTE_IOVA_VA;
                                RTE_LOG(DEBUG, EAL, "Physical
addresses are unavailable, selecting IOVA as VA mode.\n");
+#if defined(RTE_LIBRTE_KNI) && LINUX_VERSION_CODE >= KERNEL_VERSION(4, 6, 0)
+                       } else if (rte_eal_check_module("rte_kni") == 1) {
+                               iova_mode = RTE_IOVA_PA;
+                               RTE_LOG(DEBUG, EAL, "Forcing IOVA as
'PA' for better perfomance with KNI\n");
+#endif
                        } else if (is_iommu_enabled()) {
                                /* we have an IOMMU, pick IOVA as VA mode */
                                iova_mode = RTE_IOVA_VA;
@@ -1085,7 +1090,7 @@ rte_eal_init(int argc, char **argv)
                                RTE_LOG(DEBUG, EAL, "IOMMU is not
available, selecting IOVA as PA mode.\n");
                        }
                }
-#ifdef RTE_LIBRTE_KNI
-               /* Workaround for KNI which requires physical address to work */
+#if defined(RTE_LIBRTE_KNI) && LINUX_VERSION_CODE < KERNEL_VERSION(4, 6, 0)
+               /* Workaround for KNI which requires physical address
to work with kernels < 4.6 */
                if (iova_mode == RTE_IOVA_VA &&
                                rte_eal_check_module("rte_kni") == 1) {


-- 
David Marchand