On Sat, Jan 25, 2025 at 11:03:47PM +0800, Furong Xu wrote: > Hi Thierry > > 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. > > It is recommended to disable the "SPH feature" by default unless some > certain cases depend on it. Like Ido said, two large buffers being > allocated from the same page pool for each packet, this is a huge waste > of memory, and brings performance drops for most of general cases. > > Our downstream driver and two mainline drivers disable SPH by default: > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/ethernet/stmicro/stmmac/dwmac-dwc-qos-eth.c#n357 > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c#n471 Okay, that's something we can look into changing. What would be an example of a use-case depending on SPH? Also, isn't this something that should be a policy that users can configure? Irrespective of that we should fix the problems we are seeing with SPH enabled. Thierry
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