On Mon, 2009-03-09 at 08:16 +0100, Hans Verkuil wrote: > On Monday 09 March 2009 02:07:33 Trent Piepho wrote: > > On Sun, 8 Mar 2009, Hans Verkuil wrote: > > > The last one fixes an ivtv regression caused by this change: > > > > > > changeset: 10811:0a0eba8e64d5 > > > user: Trent Piepho <xyzzy@xxxxxxxxxxxxx> > > > date: Tue Mar 03 20:21:02 2009 -0800 > > > summary: videodev: only copy needed part of RW ioctl's parameter > > > > > > The fix is simple: switch on the full ioctl command instead of just the > > > NR field. > > > > > > Thanks to Martin Dauskardt for doing the bisect and tracing the > > > breakage to this change. > > > > Switching on the whole ioctl makes the switch statement a lot less > > efficient. I'd rather just put a if (_IOC_TYPE(cmd) != 'V') return 0; in > > there. That should fix the non-v4l2 ioctls, right? > > That was my first thought as well, but I realized that this is one area > where you really do not want to take any risk. > > Personally I think this code is overoptimization. In my view the performance > advantage is minimal while reducing the readability of the code. On x86_64, I counted 3 bytes per switch case saved. For the 22 switch cases: a total of 66 bytes saved. If compiled code size reduction is the efficiency measure, I suspect there are probably lower hanging fruit to be picked. Assuming a 32 byte I-cache line, the aforementioned savings saves about 2 lines worth of loading from memory. Maybe it matters for platforms with small cache sizes (embedded platforms?). Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
