On Tue, Oct 8, 2024 at 11:57 AM David Wei <dw@xxxxxxxxxxx> wrote:
>
> On 2024-10-04 03:34, Taehee Yoo wrote:
> > On Fri, Oct 4, 2024 at 3:43 AM Mina Almasry <almasrymina@xxxxxxxxxx> wrote:
> >>> @@ -3608,9 +3629,11 @@ static void bnxt_free_rx_rings(struct bnxt *bp)
> >>>
> >>> static int bnxt_alloc_rx_page_pool(struct bnxt *bp,
> >>> struct bnxt_rx_ring_info *rxr,
> >>> + int queue_idx,
> >>> int numa_node)
> >>> {
> >>> struct page_pool_params pp = { 0 };
> >>> + struct netdev_rx_queue *rxq;
> >>>
> >>> pp.pool_size = bp->rx_agg_ring_size;
> >>> if (BNXT_RX_PAGE_MODE(bp))
> >>> @@ -3621,8 +3644,15 @@ static int bnxt_alloc_rx_page_pool(struct bnxt *bp,
> >>> pp.dev = &bp->pdev->dev;
> >>> pp.dma_dir = bp->rx_dir;
> >>> pp.max_len = PAGE_SIZE;
> >>> - pp.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV;
> >>> + pp.order = 0;
> >>> +
> >>> + rxq = __netif_get_rx_queue(bp->dev, queue_idx);
> >>> + if (rxq->mp_params.mp_priv)
> >>> + pp.flags = PP_FLAG_DMA_MAP | PP_FLAG_ALLOW_UNREADABLE_NETMEM;
> >>
> >> This is not the intended use of PP_FLAG_ALLOW_UNREADABLE_NETMEM.
> >>
> >> The driver should set PP_FLAG_ALLOW_UNREADABLE_NETMEM when it's able
> >> to handle unreadable netmem, it should not worry about whether
> >> rxq->mp_params.mp_priv is set or not.
> >>
> >> You should set PP_FLAG_ALLOW_UNREADABLE_NETMEM when HDS is enabled.
> >> Let core figure out if mp_params.mp_priv is enabled. All the driver
> >> needs to report is whether it's configured to be able to handle
> >> unreadable netmem (which practically means HDS is enabled).
> >
> > The reason why the branch exists here is the PP_FLAG_ALLOW_UNREADABLE_NETMEM
> > flag can't be used with PP_FLAG_DMA_SYNC_DEV.
> >
> > 228 if (pool->slow.flags & PP_FLAG_DMA_SYNC_DEV) {
> > 229 /* In order to request DMA-sync-for-device the page
> > 230 * needs to be mapped
> > 231 */
> > 232 if (!(pool->slow.flags & PP_FLAG_DMA_MAP))
> > 233 return -EINVAL;
> > 234
> > 235 if (!pool->p.max_len)
> > 236 return -EINVAL;
> > 237
> > 238 pool->dma_sync = true; //here
> > 239
> > 240 /* pool->p.offset has to be set according to the address
> > 241 * offset used by the DMA engine to start copying rx data
> > 242 */
> > 243 }
> >
> > If PP_FLAG_DMA_SYNC_DEV is set, page->dma_sync is set to true.
> >
> > 347 int mp_dmabuf_devmem_init(struct page_pool *pool)
> > 348 {
> > 349 struct net_devmem_dmabuf_binding *binding = pool->mp_priv;
> > 350
> > 351 if (!binding)
> > 352 return -EINVAL;
> > 353
> > 354 if (!pool->dma_map)
> > 355 return -EOPNOTSUPP;
> > 356
> > 357 if (pool->dma_sync) //here
> > 358 return -EOPNOTSUPP;
> > 359
> > 360 if (pool->p.order != 0)
> > 361 return -E2BIG;
> > 362
> > 363 net_devmem_dmabuf_binding_get(binding);
> > 364 return 0;
> > 365 }
> >
> > In the mp_dmabuf_devmem_init(), it fails when pool->dma_sync is true.
>
> This won't work for io_uring zero copy into user memory. We need all
> PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV | PP_FLAG_ALLOW_UNREADABLE_NETMEM
> set.
>
> I agree with Mina that the driver should not be poking at the mp_priv
> fields. How about setting all the flags and then letting the mp->init()
> figure it out? mp_dmabuf_devmem_init() is called within page_pool_init()
> so as long as it resets dma_sync if set I don't see any issues.
>
Ah, I haven't thought the failure of PP_FLAG_DMA_SYNC_DEV
for dmabuf may be wrong.
IIUC this flag indicates sync between device and CPU.
But device memory TCP is not related to sync between device and CPU.
So, I think we need to remove this condition check code in the core.
How do you think about it?
> >
> > tcp-data-split can be used for normal cases, not only devmem TCP case.
> > If we enable tcp-data-split and disable devmem TCP, page_pool doesn't
> > have PP_FLAG_DMA_SYNC_DEV.
> > So I think mp_params.mp_priv is still useful.
> >
> > Thanks a lot,
> > Taehee Yoo
> >
> >>
> >>
> >> --
> >> Thanks,
> >> Mina
