Re: [dpdk-dev] [PATCH v3 1/3] eal/linux: select iova-mode va with no-huge option

[dwilder <dwilder@us.ibm.com>]

Thanks you for your review Jerin.  See my responses are inline.

On 2020-03-20 06:24, Jerin Jacob wrote:
> On Fri, Feb 21, 2020 at 4:22 AM David Wilder <dwilder@us.ibm.com> 
> wrote:
>> 
>> If --no-huge is set and iova-mode has not been specified force VA 
>> mode.
>> If --no-huge and --iova-mode=PA is requested error out as this is
>> an impossible configuration.
>> 
>> Signed-off-by: David Wilder <dwilder@us.ibm.com>
>> ---
>>  lib/librte_eal/linux/eal/eal.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>> 
>> diff --git a/lib/librte_eal/linux/eal/eal.c 
>> b/lib/librte_eal/linux/eal/eal.c
>> index 9530ee55f..d3a0a1731 100644
>> --- a/lib/librte_eal/linux/eal/eal.c
>> +++ b/lib/librte_eal/linux/eal/eal.c
>> @@ -1062,9 +1062,16 @@ rte_eal_init(int argc, char **argv)
>> 
>>         /* if no EAL option "--iova-mode=<pa|va>", use bus IOVA scheme 
>> */
>>         if (internal_config.iova_mode == RTE_IOVA_DC) {
>> +
>>                 /* autodetect the IOVA mapping mode */
>>                 enum rte_iova_mode iova_mode = 
>> rte_bus_get_iommu_class();
>> 
>> +               if (iova_mode == RTE_IOVA_PA && 
>> !rte_eal_has_hugepages()) {
>> +                       iova_mode = RTE_IOVA_VA;

> 
> What if igb_uio or vfio_nommu has been loaded(i.e no iommu support
> enabled from the driver)? This would fail.

Yes they would fail.  If igb_uio or vfio_nommu (or any driver) cant be 
forced to VA mode it cant be used with out hugepages.  Drivers can be 
available but not used therefor we print a warning message.

> 
>> +                       RTE_LOG(WARNING, EAL, "Some buses want 'PA' 
>> but forcing 'VA' because --no-huge is requested.\n");
>> +                       RTE_LOG(WARNING, EAL, "Not all buses may be 
>> able to initialize.\n");
>> +               }
>> +
>>                 if (iova_mode == RTE_IOVA_DC) {
>>                         RTE_LOG(DEBUG, EAL, "Buses did not request a 
>> specific IOVA mode.\n");
>> 
>> @@ -1111,6 +1118,13 @@ rte_eal_init(int argc, char **argv)
>>                         internal_config.iova_mode;
>>         }
>> 
>> +       if (rte_eal_iova_mode() == RTE_IOVA_PA &&
>> +           rte_eal_has_hugepages() == 0) {
>> +               rte_eal_init_alert("Cannot use IOVA as 'PA' with 
>> --no-huge");
> 
> Top of the tree already detecting this case. am I missing anything?
> 
> [master]dell[dpdk.org] $ sudo ./build/app/test/dpdk-test  -c 0x3
> --no-huge --iova-mode=pa
> EAL: Detected 56 lcore(s)
> EAL: Detected 2 NUMA nodes
> EAL: Static memory layout is selected, amount of reserved memory can
> be adjusted with -m or --socket-mem
> EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
> EAL: FATAL: Cannot use IOVA as 'PA' since physical addresses are not 
> available
> EAL: Cannot use IOVA as 'PA' since physical addresses are not available
> 

The check you reference is reporting that physical address are not 
available, for example no permissions to read /proc/self/pagemap.  In 
this case, if --no-huge is set then PA mode is not allowed. There is no 
guarantee that physical address are persistent with out using hugepages.


>> +               rte_errno = EINVAL;
>> +               return -1;
>> +       }
>> +
>>         if (rte_eal_iova_mode() == RTE_IOVA_PA && !phys_addrs) {
>>                 rte_eal_init_alert("Cannot use IOVA as 'PA' since 
>> physical addresses are not available");
>>                 rte_errno = EINVAL;
>> --
>> 2.25.0
>>