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    SubjectRe: How to improve the quality of the kernel?
    On Sunday, 17 June 2007 20:52, Andrew Morton wrote:
    > On Sun, 17 Jun 2007 20:53:41 +0200 Bartlomiej Zolnierkiewicz <> wrote:
    > >
    > >
    > > IMO we should concentrate more on preventing regressions than on fixing them.
    > > In the long-term preventing bugs is cheaper than fixing them afterwards.
    > >
    > > First let me tell you all a little story...
    > >
    > > Over two years ago I've reviewed some _cleanup_ patch and noticed three bugs
    > > in it (in other words I potentially prevented three regressions). I also
    > > asked for more thorough verification of the patch as I suspected that it may
    > > have more problems. The author fixed the issues and replied that he hasn't
    > > done the full verification yet but he doesn't suspect any problems...
    > >
    > > Fast forward...
    > >
    > > Year later I discover that the final version of the patch hit the mainline.
    > > I don't remember ever seeing the final version in my mailbox (there are no
    > > cc: lines in the patch description) and I saw that I'm not credited in the
    > > patch description. However the worse part is that it seems that the full
    > > verification has never been done. The result? Regression in the release
    > > kernel (exactly the issue that I was worried about) which required three
    > > patches and over a month to be fixed completely. It seems that a year
    > > was not enough to get this ~70k _cleanup_ patch fully verified and tested
    > > (it hit -mm soon before being merged)...
    > crap. Commit ID, please ;)
    > > >From reviewer's POV: I have invested my time into review, discovered real
    > > issues and as a reward I got no credit et all and extra frustration from the
    > > fact that part of my review was forgotten/ignored (the part which resulted in
    > > real regression in the release kernel)... Oh and in the past the said
    > > developer has already been asked (politely in private message) to pay more
    > > attention to his changes (after I silently fixed some other regression caused
    > > by his other patch).
    > >
    > > But wait there is more, I happend to be the maintainer of the subsystem which
    > > got directly hit by the issue and I was getting bugreports from the users about
    > > the problem... :-)
    > >
    > > It wasn't my first/last bad experience as a reviewer... finally I just gave up
    > > on reviewing other people patches unless they are stricly for IDE subsystem.
    > >
    > > The moral of the story is that currently it just doesn't pay off to do
    > > code reviews.
    > I dunno. I suspect (hope) that this was an exceptional case, hence one
    > should not draw general conclusions from it. It certainly sounds very bad.
    > > From personal POV it pays much more to wait until buggy patch
    > > hits the mainline and then fix the issues yourself (at least you will get
    > > some credit). To change this we should put more ephasize on the importance
    > > of code reviews by "rewarding" people investing their time into reviews
    > > and "rewarding" developers/maintainers taking reviews seriously.
    > >
    > > We should credit reviewers more, sometimes it takes more time/knowledge to
    > > review the patch than to make it so getting near to zero credit for review
    > > doesn't sound too attractive. Hmm, wait it can be worse - your review
    > > may be ignored... ;-)
    > >
    > > >From my side I think I'll start adding less formal "Reviewed-by" to IDE
    > > patches even if the review resulted in no issues being found (in additon to
    > > explicit "Acked-by" tags and crediting people for finding real issues - which
    > > I currently always do as a way for showing my appreciation for their work).
    > yup, Reviewed-by: is good and I do think we should start adopting it,
    > although I haven't thought through exactly how.
    > On my darker days I consider treating a Reviewed-by: as a prerequisite for
    > merging. I suspect that would really get the feathers flying.

    How about the following "algorithm":

    * Step 1: Send a patch as an RFC to the relevant lists/people and only if there
    are no negative comments within at least n days, you are allowed to proceed
    to the next step. If anyone has reviewed/acked the patch, add their names
    and email addresses as "Reviewed-by"/"Acked-by" to the patch in the next
    * Step 2: Send the patch as an RC to the relevant lists/people _and_ LKML and
    if there are no negative comments within at least n days, you can proceed to
    the next step. If anyone has reviewed/acked the patch, add their names
    and email addresses as "Reviewed-by"/"Acked-by" to the patch in the next
    * Step 3: Submit the patch for merging to the right maintainer (keeping the
    previous CC list).

    where n is a number that needs to be determined (I think that n could be 3).
    Well, "negative comments" should also be defined more precisely. ;-)

    > > I also encourage other maintainers/developers to pay more attention to
    > > adding "Acked-by"/"Reviewed-by" tags and crediting reviewers. I hope
    > > that maintainers will promote changes that have been reviewed by others
    > > by giving them priority over other ones (if the changes are on more-or-less
    > > the same importance level of course, you get the idea).
    > >
    > > Now what to do with people who ignore reviews and/or have rather high
    > > regressions/patches ratio?
    > Ignoring a review would be a wildly wrong thing to do. It's so unusual
    > that I'd be suspecting a lost email or an i-sent-the-wrong-patch.
    > As for high regressions/patches ratio: that'll be hard to calculate and
    > tends to be dependent upon the code which is being altered rather than who
    > is doing the altering: some stuff is just fragile, for various reasons.
    > One ratio which we might want to have a think about is the patches-sent
    > versus reviews-done ratio ;)
    > > I think that we should have info about regressions integrated into SCM,
    > > i.e. in git we should have optional "fixes-commit" tag and we should be
    > > able to do some reverse data colletion. This feature combined with
    > > "Author:" info after some time should give us some very interesting
    > > statistics (Top Ten "Regressors"). It wouldn't be ideal (ie. we need some
    > > patches threshold to filter out people with 1 patch and >= 1 regression(s),
    > > we need to remember that some code areas are more difficult than the others
    > > and that patches are not equal per se etc.) however I believe than making it
    > > into Top Ten "Regressors" should give the winners some motivation to improve
    > > their work ethic. Well, in the worst case we would just get some extra
    > > trivial/documentation patches. ;-)
    > We of course do want to minimise the amount of overhead for each developer.
    > I'm a strong believer in specialisation: rather than requiring that *every*
    > developer/maintainer integrate new steps in their processes it would be
    > better to allow them to proceed in a close-to-usual fashion and to provide
    > for a specialist person (or team) to do the sorts of things which you're
    > thinking about.

    Still, even very experienced developers make trivial mistakes, so there should
    be a way to catch such things before they hit -rc or even -mm kernels


    "Premature optimization is the root of all evil." - Donald Knuth
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