On 2020-10-14 12:34:25 [-0400], Alan Stern wrote: > 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.) There are no concurrent transfer. There is a bit used as a lock. The first one does the transfer, the other wait. > > 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. that is unfortunately true. Let me do the single buffer. > Alan Stern Sebastian
