On Tue, 3 Feb 2015 13:42:45 +0800 "Wang, Yalin" <Yalin.Wang@xxxxxxxxxxxxxx> wrote: > > ... > > #ifdef CHECK_BEFORE_SET > if (p[i] != times) > #endif > > ... > > ---- > One run on CPU0, reader thread run on CPU1, > Test result: > sudo ./cache_test > reader:8.426228173 > 8.672198335 > > With -DCHECK_BEFORE_SET > sudo ./cache_test_check > reader:7.537036819 > 10.799746531 > You aren't measuring the right thing. You should compare if (p[i] != x) p[i] = x; versus p[i] = x; and you should do this for two cases: a) p[i] == x b) p[i] != x The first code sequence will be slower when (p[i] != x) and faster when (p[i] == x). Next, we should instrument the kernel to work out the frequency of set_bit on an already-set bit. It is only with both these ratios that we can work out whether the patch is a net gain. My suspicion is that set_bit on an already-set bit is so rare that the patch will be a loss. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
