On Mon, Jun 21, 2010 at 10:02 AM, Glauber Costa <[email protected]> wrote: > On Fri, Jun 18, 2010 at 11:35:18AM -0700, Michael Davidson wrote: >> Yes - on some Intel platforms the roundtrip time can be as much as 1800 >> clock >> cycles - with the default test threshold of 500 cycles that always fails the >> "roundtrip > 2 * threshold" test and we exit the loop without ever having >> updated >> the delta value. >> >> Note that the actual deta on those platforms is only a few tens of cycles. >> >> Most importantly, on looking more closely at the code that was added in >> this change, it really doesn't do anything useful.(other than cause the test >> to fail on platforms where the roundtrip time his high, even if the measured >> >> delta is low). It isn't as if doing a continue at that point will give you >> another >> shot at running the test - the loop executes a fixed number of times and >> sets the result base on the "best" roundtrip time - continuing the loop >> early >> if the roundtrip time is large is pointless. >> > The first problem is that the patch was not applied in the way I sent. > > I sent: > > - for (i = 0; i < NUM_ITERS; i++) { > + while (i < NUM_ITERS) { > > ... > > + i++; > > This would guarantee that if a high roundtrip was found, we would not > count this as a valid execution. This is very different from what it is > in the repository right now, which is clearly wrong.
Ok, that was my fault. I will revert the changes. > Other than thta, if there is a platform where 2 * threshold is so common, > maybe we can change it to something bigger (maybe 5?). My main point was to > rule out > scheduling issues in userspace. When they happen, they are likely to be quite > big. > > _______________________________________________ > Autotest mailing list > [email protected] > http://test.kernel.org/cgi-bin/mailman/listinfo/autotest > -- Lucas _______________________________________________ Autotest mailing list [email protected] http://test.kernel.org/cgi-bin/mailman/listinfo/autotest
