On Tue, 3 Feb 2015 13:42:45 +0800 "Wang, Yalin" <yalin.w...@sonymobile.com>
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-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
