On Wed, Oct 14, 2020 at 06:27:14PM +0200, Sebastian Andrzej Siewior wrote: > On 2020-10-14 12:14:33 [-0400], Alan Stern wrote: > > Instead, consider using the new usb_control_msg_recv() API. But it > > might be better to allocate the buffer once and for all. > > This will still allocate and free buffer on each invocation. What about Yes. That's why I suggesting doing a single buffer allocation at the start and using it for each I/O transfer. (But I'm not familiar with this code, and I don't know if there might be multiple transfers going on concurrently.) > moving the query_buf to the begin of the struct / align it? No, thank won't work either. The key to the issue is that while some memory is mapped for DMA, the CPU must not touch it or anything else in the same cache line. If a field is a member of a data structure, the CPU might very well access a neighboring member while this one is mapped, thereby messing up the cache line. Alan Stern
