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Thu, 09 Oct 2008

An interesting observation about tbench regression.

For the last several days I bisected 26-27 kernel at least 4 times, trying to find out where the bug lives. Unfortunately all the time I ended up with some obscure patches, which do not even touch x86 arch, not talking about network. Like avr32 or s390 patches, which do not even show up in my config. And I do have kernel version changesets between the two major releases, which have 15 MB/s difference between them. I do not know how exactly bisect works (I think it is a binary search in the changesets, but for example I do not know if it enters merge commit or just gets it as one) in particular and git in general, so I will do the last try to find the problem place in the 26-27 window manually selecting changesets to try and check the result. If I will not succeed there, I will move to the 23-24 and 22-23 windows with usual bisect and return to the current tree later. I think I've found a way to run two tests in parallel, so things may run a little bit faster... Second machine just started to test 23-24, which has the biggest drop.

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