Hi, On Sat, Jan 25, 2025 at 10:43:42PM +0800, Furong Xu wrote: > Hi Ido > > On Sat, 25 Jan 2025 12:20:38 +0200, Ido Schimmel wrote: > > > On Fri, Jan 24, 2025 at 10:42:56AM +0800, Furong Xu wrote: > > > On Thu, 23 Jan 2025 22:48:42 +0100, Andrew Lunn <andrew@xxxxxxx> > > > wrote: > > > > > Just to clarify, the patch that you had us try was not intended > > > > > as an actual fix, correct? It was only for diagnostic purposes, > > > > > i.e. to see if there is some kind of cache coherence issue, > > > > > which seems to be the case? So perhaps the only fix needed is > > > > > to add dma-coherent to our device tree? > > > > > > > > That sounds quite error prone. How many other DT blobs are > > > > missing the property? If the memory should be coherent, i would > > > > expect the driver to allocate coherent memory. Or the driver > > > > needs to handle non-coherent memory and add the necessary > > > > flush/invalidates etc. > > > > > > stmmac driver does the necessary cache flush/invalidates to > > > maintain cache lines explicitly. > > > > Given the problem happens when the kernel performs syncing, is it > > possible that there is a problem with how the syncing is performed? > > > > I am not familiar with this driver, but it seems to allocate multiple > > buffers per packet when split header is enabled and these buffers are > > allocated from the same page pool (see stmmac_init_rx_buffers()). > > Despite that, the driver is creating the page pool with a non-zero > > offset (see __alloc_dma_rx_desc_resources()) to avoid syncing the > > headroom, which is only present in the head buffer. > > > > I asked Thierry to test the following patch [1] and initial testing > > seems OK. He also confirmed that "SPH feature enabled" shows up in the > > kernel log. > > BTW, the commit that added split header support (67afd6d1cfdf0) says > > that it "reduces CPU usage because without the feature all the entire > > packet is memcpy'ed, while that with the feature only the header is". > > This is no longer correct after your patch, so is there still value in > > the split header feature? With two large buffers being allocated from > > Thanks for these great insights! > > Yes, when "SPH feature enabled", it is not correct after my patch, > pp_params.offset should be updated to match the offset of split payload. > > But I would like to let pp_params.max_len remains to > dma_conf->dma_buf_sz since the sizes of both header and payload are > limited to dma_conf->dma_buf_sz by DMA engine, no more than > dma_conf->dma_buf_sz bytes will be written into a page buffer. > So my patch would be like [2]: > > BTW, the split header feature will be very useful on some certain > cases, stmmac driver should support this feature always. > > [2] > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > index edbf8994455d..def0d893efbb 100644 > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > @@ -2091,7 +2091,7 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv, > pp_params.nid = dev_to_node(priv->device); > pp_params.dev = priv->device; > pp_params.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE; > - pp_params.offset = stmmac_rx_offset(priv); > + pp_params.offset = priv->sph ? 0 : stmmac_rx_offset(priv); SPH is the only scenario in which the driver uses multiple buffers per packet? > pp_params.max_len = dma_conf->dma_buf_sz; Are you sure this is correct? Page pool documentation says that "For pages recycled on the XDP xmit and skb paths the page pool will use the max_len member of struct page_pool_params to decide how much of the page needs to be synced (starting at offset)" [1]. While "no more than dma_conf->dma_buf_sz bytes will be written into a page buffer", for the head buffer they will be written starting at a non-zero offset unlike buffers used for the data, no? [1] https://docs.kernel.org/networking/page_pool.html#dma-sync
