lkml.org 
[lkml]   [2016]   [Dec]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] doc: add note on usleep_range range
    On Tue, Dec 13, 2016 at 01:05:12PM +0100, Julia Lawall wrote:
    >
    >
    > On Tue, 13 Dec 2016, Nicholas Mc Guire wrote:
    >
    > > On Tue, Dec 13, 2016 at 11:10:50AM +0200, Jani Nikula wrote:
    > > > On Tue, 13 Dec 2016, Nicholas Mc Guire <hofrat@osadl.org> wrote:
    > > > > useleep_range() with a delta of 0 makes no sense and only prevents the
    > > > > timer subsystem from optimizing interrupts. As any user of usleep_range()
    > > > > is in non-atomic context the timer jitter is in the range of 10s of
    > > > > microseconds anyway.
    > > > >
    > > > > This adds a note making it clear that a range of 0 is a bad idea.
    > > >
    > > > So I don't really have anything to do with the timer subsystem, I'm just
    > > > their "consumer", so take this with a grain of salt.
    > > >
    > > > Documentation is good, but I don't think this will be enough.
    > > >
    > > > I think the only thing that will work is to detect and complain about
    > > > things like this automatically. Some ideas:
    > > >
    > > > * WARN_ON(min == max) or WARN_ON_ONCE(min == max) in usleep_range()
    > > > might be drastic, but it would get the job done eventually.
    > > >
    > > > * If you want to avoid the runtime overhead (and complaints about the
    > > > backtraces), you could wrap usleep_range() in a macro that does
    > > > BUILD_BUG_ON(min == max) if the parameters are build time constants
    > > > (they usually are). But you'd have to fix all the problem cases first.
    > > >
    > > > * You could try (to persuade Julia or Dan) to come up with a
    > > > cocci/smatch check for usleep_range() calls where min == max, so we
    > > > could get bug reports for this. This probably works on expressions, so
    > > > this would catch also cases where the parameters aren't built time
    > > > constants.
    > > >
    > >
    > > I fully agree - without automation it is almost usless
    > > the coccinelle spatch is a seperate patch and it is tested butnot yet
    > > submitted.
    > >
    > > the spatch for this iss actually trivial
    > >
    > > @nulldelta@
    > > constant C;
    > > position p;
    > > @@
    > >
    > > * usleep_range@p(C,C)
    >
    > People never use more complex expressions?
    >
    well yes
    @nulldelta@
    expression E;
    position p;
    @@

    * usleep_range@p(E,E)

    but that seems to be it.
    and the vast majority is simply constants

    thx!
    hofrat

    \
     
     \ /
      Last update: 2016-12-13 13:24    [W:4.004 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site