From: Alexander Duyck <[email protected]> Date: Fri, 21 Apr 2017 08:07:45 -0700
> On Fri, Apr 21, 2017 at 7:20 AM, Jakub Kicinski > <[email protected]> wrote: >> DMA unmap may destroy changes CPU made to the buffer. To make XDP >> run correctly on non-x86 platforms we should use the >> DMA_ATTR_SKIP_CPU_SYNC attribute. >> >> Thanks to using the attribute we can now push the sync operation to >> the common code path from XDP handler. >> >> A little bit of variable name reshuffling is required to bring the >> code back to readable state. >> >> Signed-off-by: Jakub Kicinski <[email protected]> > > So I see where you added the sync_single_for_cpu, but what about the > sync_single_for_device? It needs to be called for the buffer before > you assign it for Rx. On x86 it won't really matter but for proper > utilization of the DMA API you need to sync the buffer even for Rx > just to make certain that the cache lines are evicted prior to the > device attempting to write to the buffer. Agreed, a sync before giving the buffer to the device is necessary.
