Messages in this thread | | | Date | Mon, 5 Dec 2022 15:24:12 +0000 | Subject | Re: [PATCH v3] perf jevents: Parse metrics during conversion | From | John Garry <> |
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On 01/12/2022 03:41, Ian Rogers wrote: > Currently the 'MetricExpr' json value is passed from the json > file to the pmu-events.c. This change introduces an expression > tree that is parsed into. The parsing is done largely by using > operator overloading and python's 'eval' function. Two advantages > in doing this are: > > 1) Broken metrics fail at compile time rather than relying on > `perf test` to detect. `perf test` remains relevant for checking > event encoding and actual metric use.
Do we still require the code to "resolve metrics" in resolve_metric()? But I'm not sure it even ever had any users.
> > 2) The conversion to a string from the tree can minimize the metric's > string size, for example, preferring 1e6 over 1000000, avoiding > multiplication by 1 and removing unnecessary whitespace. On x86 > this reduces the string size by 3,050bytes (0.07%).
Out of curiosity, did you try the exponent change on its own (to see the impact on size)?
Nit:
Unrelated, really, I notice that sometimes we lose the parenthesis and sometimes never had them, like:
/* offset=11526 */ "\000\000metrics\000Ave [...] 0\000( 1000000000 * ( UNC_CHA /* offset=11207 */ "\000\000metrics\000Ave [...] 0\0001e9 * (UNC_CHA_TOR
To me, it seems neater to have the expression contained within (a parenthesis) ever since we moved to this "big string". This seems to be a preexisting feature.
Thanks, John
> > In future changes it would be possible to programmatically > generate the json expressions (a single line of text and so a > pain to write manually) for an architecture using the expression > tree. This could avoid copy-pasting metrics for all architecture > variants. > > Signed-off-by: Ian Rogers<irogers@google.com>
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