From: Herbert Xu > Sent: 20 March 2017 13:16 > On Mon, Mar 20, 2017 at 11:39:37AM +0100, Peter Zijlstra wrote: > > > > Can we at least give a benchmark and have someone run numbers? We should > > be able to quantify these things. > > Do you realise how many times this thing gets hit at 10Gb/s or > higher? Anyway, since you're proposing this change you should > demonstrate that it does not cause a performance regression. What checks does refcnt_t actually do? An extra decrement is hard to detect since the item gets freed early. I guess making the main 'allocate/free' code hold (say) 64k references would give some leeway for extra decrements. An extra increment will be detected when the count eventually wraps. Unless the error is in a very common path that won't happen for a long time. On x86 the cpu flags from the 'lock inc/dec' could be used to reasonably cheaply detect errors - provided you actually generate a forwards branch. Otherwise having a common, but not every packet, code path verify that the reference count is 'sane' would give reasonable coverage. David
