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    SubjectRe: How to improve the quality of the kernel?
    On 17/06/07, Bartlomiej Zolnierkiewicz <> wrote:
    > Hi,
    > On Sunday 17 June 2007, Adrian Bunk wrote:
    > > On Sun, Jun 17, 2007 at 03:17:58PM +0200, Michal Piotrowski wrote:
    > > > On 17/06/07, Adrian Bunk <> wrote:
    > > >...
    > > >> Fine with me, but:
    > > >>
    > > >> There are not so simple cases like big infrastructure patches with
    > > >> 20 other patches in the tree depending on it causing a regression, or
    > > >> even worse, a big infrastructure patch exposing a latent old bug in some
    > > >> completely different area of the kernel.
    > > >
    > > > It is different case.
    > > >
    > > > "If the patch introduces a new regression"
    > > >
    > > > introduces != exposes an old bug
    > >
    > > My remark was meant as a note "this sentence can't handle all
    > > regressions" (and for a user it doesn't matter whether a new
    > > regression is introduced or an old regression exposed).
    > >
    > > It could be we simply agree on this one. ;-)
    > >
    > > > Removal of 20 patches will be painful, but sometimes you need to
    > > > "choose minor evil to prevent a greater one" [1].
    > > >
    > > >> And we should be aware that reverting is only a workaround for the real
    > > >> problem which lies in our bug handling.
    > > >...
    > >
    > > And this is something I want to emphasize again.
    > >
    > > How can we make any progress with the real problem and not only the
    > > symptoms?
    > >
    > > There's now much money in the Linux market, and the kernel quality
    > > problems might result in real costs in the support of companies like
    > > IBM, SGI, Redhat or Novell (plus it harms the Linux image which might
    > > result in lower revenues).
    > >
    > > If [1] this is true, it might even pay pay off for them to each assign
    > > X man hours per month of experienced kernel developers to upstream
    > > kernel bug handling?
    > >
    > > This is just a wild thought and it might be nonsense - better
    > > suggestions for solving our quality problems would be highly welcome...
    > 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)...
    > 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. 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).
    > 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).

    I think that this is a very good idea - especially for large, intrusive patches.
    Long {Acked,Reviewed,Signed-off,Tested}-by list will be welcome.

    > Now what to do with people who ignore reviews and/or have rather high
    > regressions/patches 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. ;-)
    > Sorry for a bit chaotic mail but I hope that message is clear.
    > Thanks,
    > Bart


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