From: Kalesh Singh <kaleshsingh@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>,
Hridya Valsaraju <hridya@google.com>,
Namhyung Kim <namhyung@kernel.org>,
Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Shuah Khan <shuah@kernel.org>, Tom Zanussi <zanussi@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH 1/5] tracing: Add support for creating hist trigger variables from literal
Date: Tue, 19 Oct 2021 14:21:04 -0700 [thread overview]
Message-ID: <CAC_TJvfT-1SeEhDnVjRfcv1SjKmZbcdy=cBVXYeB1GLTv+=e+w@mail.gmail.com> (raw)
In-Reply-To: <20211019164834.465b2a53@gandalf.local.home>
On Tue, Oct 19, 2021 at 1:48 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 15 Sep 2021 19:52:45 +0000
> Kalesh Singh <kaleshsingh@google.com> wrote:
>
> > Currently hist trigger expressions don't support the use of numeric
> > literals:
> > e.g. echo 'hist:keys=common_pid:x=$y-1234'
> > --> is not valid expression syntax
> >
> > Having the ability to use numeric constants in hist triggers supports
> > a wider range of expressions for creating variables.
>
> I'm not against the patch, but I'm curious to what use case this would be
> useful for. In the cover letter it mentions the division and multiplication
> for finding associated buckets, but what is the addition / subtraction used
> for?
Addition and subtraction are already supported operations. The use
case given in Documentation/trace/histogram.rst is for calculating
latencies. I don't have a use case where the constants may be needed
in the addition/subtraction, but for simplicity and completeness we
support them for all operations.
- Kalesh
>
> -- Steve
>
>
> >
> > Add support for creating trace event histogram variables from numeric
> > literals.
> >
> > e.g. echo 'hist:keys=common_pid:x=1234,y=size-1024' >> event/trigger
> >
> > A negative numeric constant is created, using unary minus operator
> > (parentheses are required).
> >
> > e.g. echo 'hist:keys=common_pid:z=-(2)' >> event/trigger
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> >
next prev parent reply other threads:[~2021-10-19 21:21 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-15 19:52 [PATCH 0/5] tracing: Extend histogram triggers expression parsing Kalesh Singh
2021-09-15 19:52 ` [PATCH 1/5] tracing: Add support for creating hist trigger variables from literal Kalesh Singh
2021-10-19 20:48 ` Steven Rostedt
2021-10-19 21:21 ` Kalesh Singh [this message]
2021-10-19 21:26 ` Steven Rostedt
2021-10-19 21:49 ` Kalesh Singh
2021-09-15 19:52 ` [PATCH 2/5] tracing: Add division and multiplication support for hist triggers Kalesh Singh
2021-10-19 20:45 ` Steven Rostedt
2021-10-19 21:24 ` Kalesh Singh
2021-09-15 19:52 ` [PATCH 3/5] tracing: Fix operator precedence for hist triggers expression Kalesh Singh
2021-09-15 19:52 ` [PATCH 4/5] tracing/selftests: Add tests for hist trigger expression parsing Kalesh Singh
2021-09-15 19:52 ` [PATCH 5/5] tracing/histogram: Document expression arithmetic and constants Kalesh Singh
2021-09-15 20:09 ` [PATCH 0/5] tracing: Extend histogram triggers expression parsing Kalesh Singh
2021-09-30 22:58 ` Namhyung Kim
2021-10-02 0:54 ` Kalesh Singh
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