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    SubjectRe: [PATCH] RAS: Add a tracepoint for reporting memory controller events
    On Thu, May 31, 2012 at 03:04:55PM -0300, Mauro Carvalho Chehab wrote:
    > The tracepoint approach is proposed as a way to replace dmesg, so,
    > dmesg is not an option.

    Of course it is an option: userspace parses dmesg and gets grain value.

    > Sysfs nodes for address grain won't work, as, on MCA, the grain is
    > only known when an error is generated, and it is valid only together
    > with an error report.

    This is only true on Intel.

    > Having the _same_ field exported either in sysfs or via the trace,
    > depending if the grain is dynamic or if it is global-wide is a very
    > crappy API, as the same information would be provided to userspace via
    > different API's, with is insane.

    No, what is crappy is "punishing" other drivers just because you need
    grain for your drivers.

    Ask Steven how expensive are 4 bytes in a tracepoint and what it means
    wasting space in the ring buffer.

    [ … ]

    > > Again, only on those drivers which have dynamic grain. Other drivers
    > > which keep outputting 'x' (and 'x' doesn't change) on every tracepoint
    > > invocation don't need to output it all in the tracepoint.
    >
    > So what? If only one type of granularity applies to all addresses, the
    > information provided to userspace won't be wrong.

    The argument is not whether it is wrong or not - it is about wasting
    space unnecessarily where it counts. Write this down and hammer it to
    your forehead so that you can finally understand it!

    <remove some random unrelated blubber>

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