Re: [dpdk-dev] [PATCH 5/7] mem: modify error message for DMA mask check

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Thu, Nov 1, 2018 at 10:29 AM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 31-Oct-18 5:29 PM, Alejandro Lucero wrote:
> > If DMA mask checks shows mapped memory out of the supported range
> > specified by the DMA mask, nothing can be done but return an error
> > an report the error. This can imply the app not being executed at
> > all or precluding dynamic memory allocation once the app is running.
> > In any case, we can advice the user to force IOVA as PA if currently
> > IOVA being VA and user being root.
> >
> > Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>
> > ---
>
> General comment - legacy memory will also need this check, correct?
>
>
Yes, there is another patch adding this for both, legacy-mem and no-huge
options.


> >   lib/librte_eal/common/malloc_heap.c | 35 +++++++++++++++++++++++++----
> >   1 file changed, 31 insertions(+), 4 deletions(-)
> >
> > diff --git a/lib/librte_eal/common/malloc_heap.c
> b/lib/librte_eal/common/malloc_heap.c
> > index 7d423089d..711622f19 100644
> > --- a/lib/librte_eal/common/malloc_heap.c
> > +++ b/lib/librte_eal/common/malloc_heap.c
> > @@ -5,8 +5,10 @@
> >   #include <stddef.h>
> >   #include <stdlib.h>
> >   #include <stdio.h>
> > +#include <unistd.h>
> >   #include <stdarg.h>
> >   #include <errno.h>
> > +#include <sys/types.h>
> >   #include <sys/queue.h>
> >
> >   #include <rte_memory.h>
> > @@ -294,7 +296,6 @@ alloc_pages_on_heap(struct malloc_heap *heap,
> uint64_t pg_sz, size_t elt_size,
> >       size_t alloc_sz;
> >       int allocd_pages;
> >       void *ret, *map_addr;
> > -     uint64_t mask;
> >
> >       alloc_sz = (size_t)pg_sz * n_segs;
> >
> > @@ -322,11 +323,37 @@ alloc_pages_on_heap(struct malloc_heap *heap,
> uint64_t pg_sz, size_t elt_size,
> >               goto fail;
> >       }
> >
> > +     /* Once we have all the memseg lists configured, if there is a dma
> mask
> > +      * set, check iova addresses are not out of range. Otherwise the
> device
> > +      * setting the dma mask could have problems with the mapped memory.
> > +      *
> > +      * There are two situations when this can happen:
> > +      *      1) memory initialization
> > +      *      2) dynamic memory allocation
> > +      *
> > +      * For 1), an error when checking dma mask implies app can not be
> > +      * executed. For 2) implies the new memory can not be added.
> > +      */
> >       if (mcfg->dma_maskbits) {
> >               if (rte_mem_check_dma_mask(mcfg->dma_maskbits)) {
> > -                     RTE_LOG(ERR, EAL,
> > -                             "%s(): couldn't allocate memory due to DMA
> mask\n",
> > -                             __func__);
> > +                     /* Currently this can only happen if IOMMU is
> enabled
> > +                      * with RTE_ARCH_X86. It is not safe to use this
> memory
> > +                      * so returning an error here.
>
> I don't think it's RTE_ARCH_X86-only. It can be any other arch with an
> IOMMU that's reporting addressing limitations.
>

Right, but it is just IOMMU hardware from this architecture having the
current limitation.
I was trying to just explain why this can happen but I can remove the
reference to specific
 architecture problems.


> > +                      *
> > +                      * If IOVA is VA, advice to try with '--iova-mode
> pa'
> > +                      * which could solve some situations when IOVA VA
> is not
> > +                      * really needed.
> > +                      */
> > +                     uid_t user = getuid();
> > +                     if ((rte_eal_iova_mode() == RTE_IOVA_VA) && user
> == 0)
>
> rte_eal_using_phys_addrs()?
>
> (the above function name is a bit of a misnomer, it really checks if
> they are available, but not necessarily used - it will return true in
> RTE_IOVA_VA mode if you're running as root)
>

rte_eal_iova_mode returns rte_eal_get_configuration()->iova_mode what
 is set during initialization. It can be PA not just because IOMMU (not
after the patch)
but because some PMD does not reports IOVA VA support or because UIO is in
use.
Checking for root is because IOVA PA can not be used if non root.


> > +                             RTE_LOG(ERR, EAL,
> > +                                     "%s(): couldn't allocate memory
> due to DMA mask.\n"
> > +                                     "Try with 'iova-mode=pa'\n",
> > +                                     __func__);
> > +                     else
> > +                             RTE_LOG(ERR, EAL,
> > +                                     "%s(): couldn't allocate memory
> due to DMA mask\n",
> > +                                     __func__);
>
> I don't think the error message is terribly descriptive. Looking at it
> through the eyes of someone who sees it for the first time and who has
> no idea what "iova-mode=pa" is, i think it would be more useful to word
> it the following way:
>
> couldn't allocate memory due to IOVA exceeding limits of current DMA mask.
> [for non-using phys addrs case] Please try initializing EAL with
> --iova-mode=pa parameter.
>
>
I'm happy with using your terrific description instead ;-)
Thanks!


> Also, generally newlines in RTE_LOG look ugly unless you indent the line :)
>
> >                       goto fail;
> >               }
> >       }
> >
>
>
> --
> Thanks,
> Anatoly
>