Re: [Xen-devel] [PATCH v7 4/5] xen: add per-cpu buffer option to debugtrace

[Jan Beulich <jbeulich@suse.com>]

On 09.09.2019 11:25, 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@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
albeit preferably with the __read_mostly added as indicated in
reply to v6 (can still be done while committing).

> ---
> V2:
> - only allocate buffer if not already done so
> V4:
> - unsigned int -> unsigned long (Jan Beulich)
> - replace check for bytes < PAGE_SIZE by !bytes (Jan Beulich)
> - print info which buffer allocation failed (Jan Beulich)
> - replace switch by if in cpu notifier handler (Jan Beulich)
> V5:
> - don't silently ignore trailing characters when parsing buffer size
>   (Jan Beulich)
> - limit scope of some variables (Jan Beulich)
> - adjust error message format (Jan Beulich)
> V6:
> - move calculation of final debugtrace_bytes value to parameter parsing

V7: ...

Jan

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