Re: [Xen-devel] [PATCH v6 4/5] xen: add per-cpu buffer option to debugtrace

[Juergen Gross <jgross@xxxxxxxx>]

On 09.09.19 10:04, Jan Beulich wrote:
> On 09.09.2019 09:59, Jan Beulich wrote:
> > On 09.09.2019 09:35, Juergen Gross wrote:
> > > debugtrace is normally writing trace entries into a single trace
> > > buffer. There are cases where this is not optimal, e.g. when hunting
> > > a bug which requires writing lots of trace entries and one cpu is
> > > stuck. This will result in other cpus filling the trace buffer and
> > > finally overwriting the interesting trace entries of the hanging cpu.
> > >
> > > In order to be able to debug such situations add the capability to use
> > > per-cpu trace buffers. This can be selected by specifying the
> > > debugtrace boot parameter with the modifier "cpu:", like:
> > >
> > >    debugtrace=cpu:16
> > >
> > > At the same time switch the parsing function to accept size modifiers
> > > (e.g. 4M or 1G).
> > >
> > > Printing out the trace entries is done for each buffer in order to
> > > minimize the effort needed during printing. As each entry is prefixed
> > > with its sequence number sorting the entries can easily be done when
> > > analyzing them.
> > >
> > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Oh, no - I have to take this back. Looking at patch 5 I notice
> that you now only ever write last_cpu; you must have lost its
> consumer.
Oh, indeed. Thanks for spotting that. Will send out a corrected patch
soon.


Juergen

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