Hi David On 12.5.2025 18.07, David Wang wrote:
--- I was checking memory allocation behaviors (via memory profiling[1]), when I notice a high frequent memory allocation in xhci_urb_enqueue, about 250/s when using a USB webcam. If those alloced buffer could be kept and reused, lots of memory allocations could be avoid over time. This patch is just a POC, about 0/s memory allocation in xhci with this patch, when I use my USB devices, webcam/keyboard/mouse.
Thanks for looking at this, this is something that obviously needs more attention
A dynamic cached memory would be better: URB keep host controller's private data, if larger size buffer needed for private data, old buffer released and a larger buffer alloced. I did not observe any nagative impact with xhci's 250/s allocations when using my system, hence no measurement of how useful this changes can make to user. Just want to collect feedbacks before putting more effort.
I think we can make a xhci internal solution that doesn't affect other hosts or usb core. How about adding a list of struct urb_priv nodes for every usb device, or maybe even per endpoint? i.e. to struct xhci_virt_device or struct xhci_virt_ep. Add size and list_head entries to struct urb_priv. In xhci_urb_enqueue() pick the first urb_priv node from list if it exists and is large enough, otherwise just allocate a new one and set the size. When giving back the URB zero everything in the struct urb_priv except the size, and add it to the list. When the device is freed there shouldn't be any nodes left in the list, but if there are then warn and free them. Isoc transfers are the ones with odd urb_priv sizes. If we have a per device or per endpoint urb_priv list then sizes will match better. Thanks Mathias
