On Thu, 23 Jan 2025 11:53:21 -0800, Brad Griffis <bgriffis@xxxxxxxxxx> wrote: > On 1/23/25 08:35, Furong Xu wrote: > > What is the MTU of Tegra234 and NFS server? Are they both 1500? > > I see the same issue. Yes, both are 1500. > > > Could you please try attached patch to confirm if this regression is > > fixed? > > Patch fixes the issue. > > > If the attached patch fixes this regression, and so it seems to be a > > cache coherence issue specific to Tegra234, since this patch avoid > > memcpy and the page buffers may be modified by upper network stack of > > course, then cache lines of page buffers may become dirty. But by > > reverting this patch, cache lines of page buffers never become dirty, > > this is the core difference. > > Thanks for these insights. I don't have specific experience in this > driver, but I see we have dma-coherent turned on for this driver in our > downstream device tree files (i.e. dtbs that coincide with our > out-of-tree implementation of this driver). I went back to the original > code and verified that the issue was there. I did a new test where I > added dma-coherent to this ethernet node in the dtb and retested. It worked! > > 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? It is not an actual fix, it is only for diagnostic purposes. > So perhaps the only fix needed is to add dma-coherent to our device tree? Yes, add dma-coherent to ethernet node is the correct fix.
