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tracing: Improve benchmark test performance by using do_div()

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Partially revert commit d6cb38e108 ("tracing: Use div64_u64() instead
of do_div()") and use do_div() again to utilize its faster 64-by-32
division compared to the 64-by-64 division done by div64_u64().

Explicitly cast the divisor bm_cnt to u32 to prevent a Coccinelle
warning reported by do_div.cocci. The warning was removed with commit
d6cb38e108 ("tracing: Use div64_u64() instead of do_div()").

Using the faster 64-by-32 division and casting bm_cnt to u32 is safe
because we return early from trace_do_benchmark() if bm_cnt > UINT_MAX.
This approach is already used twice in trace_do_benchmark() when
calculating the standard deviation:

	do_div(stddev, (u32)bm_cnt);
	do_div(stddev, (u32)bm_cnt - 1);

Link: https://lore.kernel.org/linux-trace-kernel/20240329160229.4874-2-thorsten.blum@toblux.com

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Thorsten Blum 2024-03-29 17:02:30 +01:00 committed by Steven Rostedt (Google)
parent 33f137143e
commit 347bd7f072
1 changed files with 1 additions and 1 deletions
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2
kernel/trace/trace_benchmark.c
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@ -104,7 +104,7 @@ static void trace_do_benchmark(void)
stddev = 0; stddev = 0;
delta = bm_total; delta = bm_total;
delta = div64_u64(delta, bm_cnt); do_div(delta, (u32)bm_cnt);
avg = delta; avg = delta;
if (stddev > 0) { if (stddev > 0) {