From: Steven Rostedt <rostedt@goodmis.org>
To: Kalesh Singh <kaleshsingh@google.com>
Cc: surenb@google.com, hridya@google.com, namhyung@kernel.org,
kernel-team@android.com, Jonathan Corbet <corbet@lwn.net>,
Ingo Molnar <mingo@redhat.com>, Shuah Khan <shuah@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Tom Zanussi <zanussi@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 6/8] tracing/histogram: Optimize division by a power of 2
Date: Tue, 26 Oct 2021 23:15:57 -0400 [thread overview]
Message-ID: <20211026231557.1eedad9b@rorschach.local.home> (raw)
In-Reply-To: <20211026222123.5e206fcf@rorschach.local.home>
On Tue, 26 Oct 2021 22:21:23 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> I'm sure there's an algorithm somewhere that can give as the real max.
You got me playing with this more ;-)
OK, I added the rounding in the wrong place. I found that we can make
the max_div to be the same as the shift! The bigger the shift, the
bigger the max!
mult = (1 << shift) / div;
max_div = (1 << shift)
But the rounding needs to be with the mult / shift:
return (val * mult + ((1 << shift) - 1)) >> shift;
When val goes pass 1 << shift, then the error will be off by more than
one.
-- Steve
next prev parent reply other threads:[~2021-10-27 3:16 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-25 20:08 [PATCH v4 0/8] tracing: Extend histogram triggers expression parsing Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 1/8] tracing: Add support for creating hist trigger variables from literal Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 2/8] tracing: Add division and multiplication support for hist triggers Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 3/8] tracing: Fix operator precedence for hist triggers expression Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 4/8] tracing/histogram: Simplify handling of .sym-offset in expressions Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 5/8] tracing/histogram: Covert expr to const if both operands are constants Kalesh Singh
2021-10-25 20:08 ` [PATCH v4 6/8] tracing/histogram: Optimize division by a power of 2 Kalesh Singh
2021-10-26 19:14 ` Steven Rostedt
2021-10-26 23:39 ` Kalesh Singh
2021-10-27 0:18 ` Steven Rostedt
2021-10-27 1:09 ` Kalesh Singh
2021-10-27 1:15 ` Steven Rostedt
2021-10-27 1:31 ` Kalesh Singh
2021-10-27 2:21 ` Steven Rostedt
2021-10-27 3:15 ` Steven Rostedt [this message]
2021-10-27 4:04 ` Kalesh Singh
2021-10-27 14:06 ` Steven Rostedt
2021-10-25 20:08 ` [PATCH v4 7/8] tracing/selftests: Add tests for hist trigger expression parsing Kalesh Singh
2021-10-26 12:43 ` Masami Hiramatsu
2021-10-26 14:28 ` Kalesh Singh
2021-10-26 21:44 ` Steven Rostedt
2021-10-26 23:36 ` Kalesh Singh
2021-10-27 0:20 ` Steven Rostedt
2021-10-27 1:15 ` Kalesh Singh
2021-10-27 3:14 ` Masami Hiramatsu
2021-10-27 4:27 ` Kalesh Singh
2021-10-27 14:31 ` Steven Rostedt
2021-10-27 14:52 ` Masami Hiramatsu
2021-10-27 15:01 ` Steven Rostedt
2021-10-27 15:50 ` Steven Rostedt
2021-10-27 15:55 ` Kalesh Singh
2021-10-27 17:17 ` Steven Rostedt
2021-10-27 2:34 ` Masami Hiramatsu
2021-10-27 17:36 ` Steven Rostedt
2021-10-26 15:07 ` Steven Rostedt
2021-10-29 6:48 ` [tracing/selftests] cfece71411: kernel-selftests.ftrace.event_trigger_-_test_inter-event_histogram_trigger_onchange_action.fail kernel test robot
2021-10-29 12:00 ` Masami Hiramatsu
2021-10-29 13:10 ` Steven Rostedt
2021-11-01 3:43 ` [LKP] " Li Zhijian
2021-10-25 20:08 ` [PATCH v4 8/8] tracing/histogram: Document expression arithmetic and constants Kalesh Singh
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