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    SubjectRe: [PATCH 1/2] panic: ratelimit panic messages
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    On Thu, Jan 6, 2011 at 6:51 AM, Andrew Morton <akpm@linux-foundation.org> wrote:
    > On Tue,  4 Jan 2011 22:38:30 -0500
    > Don Zickus <dzickus@redhat.com> wrote:
    >
    >> Sometimes when things go bad, so much spew is coming on the console it is hard
    >> to figure out what happened.  This patch allows you to ratelimit the panic
    >> messages with the intent that the first panic message will provide the info
    >> we need to figure out what happened.
    >>
    >> Adds new kernel param 'panic_ratelimit=on/<integer in seconds>'
    >>
    >
    > Terminological whinge: panic() is a specific kernel API which ends up
    > doing a sort-of-oops thing.  So the graph is
    >
    >        panic           -> oops
    >        other-things    -> oops
    >
    > Your patch doesn't affect only panics - it also affects oops, BUG(),
    > etc.  So I'd suggest that this patch should do s/panic/oops/g.
    >
    >> ---
    >>  Documentation/kernel-parameters.txt |    6 ++++++
    >>  kernel/panic.c                      |   30 ++++++++++++++++++++++++++++++
    >>  2 files changed, 36 insertions(+), 0 deletions(-)
    >>
    >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    >> index 316c723..1416964 100644
    >> --- a/Documentation/kernel-parameters.txt
    >> +++ b/Documentation/kernel-parameters.txt
    >> @@ -1807,6 +1807,12 @@ and is between 256 and 4096 characters. It is defined in the file
    >>       panic=          [KNL] Kernel behaviour on panic
    >>                       Format: <timeout>
    >>
    >> +     panic_ratelimit=        [KNL] ratelimit the panic messages
    >> +                     Useful for slowing down multiple panics to capture
    >> +                     the first one before it scrolls off the screen
    >> +                     Format: "on" or some integer in seconds
    >> +                     "on" defaults to 10 minutes
    >> +
    >
    > We keep on hacking away at this and things never seem to get much
    > better.  It's still the case that a large number of our oops reports
    > are damaged because the important parts of the oops trace scrolled off
    > the screen.
    >
    > I therefore propose
    >
    >        oops_lines_delay=N,M
    >
    > which will cause the kernel to pause for M milliseconds after emitting
    > N lines of oops output.  Bonus marks for handling linewrap!

    I ever try to do similar things to printk_delay, something like
    printk_lines_delay,
    or give printk_delay one more parameter of lines.

    What do you think about this approach?

    >
    > Start the line counter at oops_begin() or thereabouts and then do the
    > delay after N lines have been emitted.  I guess that counter should
    > _not_ be invalidated in oops_end(): if the oops generates 12 lines and
    > then another 100 lines of random printk crap are printed, we still want
    > to put a pause after the 13th line of that random crap, so we can view
    > the oops.
    >
    > The oops_lines_delay implemetnation should count lines from all CPUs
    > and should block all CPUs during the delay.
    >
    > I think this would solve the problem which you're seeing, as well as
    > the much larger my-oops-scrolled-off problem?
    >
    > --
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    --
    Regards
    dave
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