Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] tracing: Explicitly cast divisor to fix Coccinelle warning | From | Thorsten Blum <> | Date | Wed, 20 Mar 2024 17:30:00 +0100 |
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On 20. Mar 2024, at 16:01, Thorsten Blum <thorsten.blum@toblux.com> wrote: > > Coccinelle also finds this one, but please ignore this patch as I just realized > this was already fixed in another patch of mine from February. > > Sorry for the inconvenience. > > Link: https://lore.kernel.org/linux-kernel/20240225164507.232942-2-thorsten.blum@toblux.com/
Actually, I will submit a new patch to revert
delta = div64_u64(delta, bm_cnt);
back to
do_div(delta, bm_cnt);
but this time include an explicit cast to u32
do_div(delta, (u32)bm_cnt);
to remove the Coccinelle warning reported by do_div.cocci and to improve performance.
The do_div() macro does a 64-by-32 division which is faster than the 64-by-64 division done by div64_u64(). Casting the divisor bm_cnt to u32 is safe since we return early from trace_do_benchmark() if bm_cnt > UINT_MAX (something I missed in d6cb38e10810).
This approach is already used when calculating the standard deviation:
do_div(stddev, (u32)bm_cnt); do_div(stddev, (u32)bm_cnt - 1);
Thanks, Thorsten
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