> Nitpick: by putting some integers after a u8, you are creating a hole
> for 3 bytes between gs_usb->active_channels and gs_usb->pipe_in, as
> shown by the pahole tool:
>
> $ pahole --class_name=gs_usb drivers/net/can/usb/gs_usb.o
> struct gs_usb {
> struct gs_can * canch[3]; /* 0 24 */
> struct usb_anchor rx_submitted; /* 24 56 */
>
> /* XXX last struct has 4 bytes of padding, 31 bits of padding */
>
> /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
> struct usb_device * udev; /* 80 8 */
> struct cyclecounter cc; /* 88 24 */
> struct timecounter tc; /* 112 40 */
> /* --- cacheline 2 boundary (128 bytes) was 24 bytes ago --- */
> spinlock_t tc_lock; /* 152 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> struct delayed_work timestamp; /* 160 88 */
>
> /* XXX last struct has 4 bytes of padding */
>
> /* --- cacheline 3 boundary (192 bytes) was 56 bytes ago --- */
> unsigned int hf_size_rx; /* 248 4 */
> u8 active_channels; /* 252 1 */
>
> /* XXX 3 bytes hole, try to pack */
>
> /* --- cacheline 4 boundary (256 bytes) --- */
> unsigned int pipe_in; /* 256 4 */
> unsigned int pipe_out; /* 260 4 */
>
> /* size: 264, cachelines: 5, members: 11 */
> /* sum members: 257, holes: 2, sum holes: 7 */
> /* member types with bit paddings: 1, total: 31 bits */
> /* paddings: 2, sum paddings: 8 */
> /* last cacheline: 8 bytes */
> };
>
> This 3 bytes hole will always exist even if you group the integers
> together (because the padding also occurs at the end of the structure)
> *but*, it is easier to maintain if the hole is at the end.
>
> So, in summary, do it like this:
>
> unsigned int hf_size_rx;
> + unsigned int pipe_in;
> + unsigned int pipe_out;
> u8 active_channels;
> };
>
> Note that there is also 2 other 4 bytes holes, so a packing
> optimization could be done here, but this is out of scope of your
> patch. If you want to address that, it must go in a different patch
> because, this time, it is another "logical change".
Thank you Vincent for this optional nitpick. For sake of simplicity
I would prefer to skip this change, but I've got your point about additional "logical change".
