kernel/trace/trace_benchmark.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Explicitly cast the divisor to u32 to fix a Coccinelle/coccicheck warning
reported by do_div.cocci.
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
kernel/trace/trace_benchmark.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
index 54d5fa35c90a..218b40050629 100644
--- a/kernel/trace/trace_benchmark.c
+++ b/kernel/trace/trace_benchmark.c
@@ -105,7 +105,7 @@ static void trace_do_benchmark(void)
stddev = 0;
delta = bm_total;
- do_div(delta, bm_cnt);
+ do_div(delta, (u32)bm_cnt);
avg = delta;
if (stddev > 0) {
--
2.44.0On Mon, 18 Mar 2024 11:52:44 +0100
Thorsten Blum <thorsten.blum@toblux.com> wrote:
> Explicitly cast the divisor to u32 to fix a Coccinelle/coccicheck warning
> reported by do_div.cocci.
>
Hmm, strange, trace_do_benchmark() has another do_div(u64, u64).
do {
last_seed = seed;
seed = stddev;
if (!last_seed)
break;
do_div(seed, last_seed);
seed += last_seed;
do_div(seed, 2);
} while (i++ < 10 && last_seed != seed);
Didn't Coccinelle find that?
Thank you,
> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
> ---
> kernel/trace/trace_benchmark.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
> index 54d5fa35c90a..218b40050629 100644
> --- a/kernel/trace/trace_benchmark.c
> +++ b/kernel/trace/trace_benchmark.c
> @@ -105,7 +105,7 @@ static void trace_do_benchmark(void)
> stddev = 0;
>
> delta = bm_total;
> - do_div(delta, bm_cnt);
> + do_div(delta, (u32)bm_cnt);
> avg = delta;
>
> if (stddev > 0) {
> --
> 2.44.0
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
On 20. Mar 2024, at 11:27, Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
>
> Hmm, strange, trace_do_benchmark() has another do_div(u64, u64).
>
> do {
> last_seed = seed;
> seed = stddev;
> if (!last_seed)
> break;
> do_div(seed, last_seed);
> seed += last_seed;
> do_div(seed, 2);
> } while (i++ < 10 && last_seed != seed);
>
> Didn't Coccinelle find that?
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/
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
Partially revert commit d6cb38e10810 ("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
d6cb38e10810 ("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);
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
Changes in v2:
- Update patch with latest changes from master
- Update patch title and description
---
kernel/trace/trace_benchmark.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
index 811b08439406..e19c32f2a938 100644
--- a/kernel/trace/trace_benchmark.c
+++ b/kernel/trace/trace_benchmark.c
@@ -104,7 +104,7 @@ static void trace_do_benchmark(void)
stddev = 0;
delta = bm_total;
- delta = div64_u64(delta, bm_cnt);
+ do_div(delta, (u32)bm_cnt);
avg = delta;
if (stddev > 0) {
--
2.44.0Partially revert commit d6cb38e10810 ("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
d6cb38e10810 ("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);
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
Changes in v2:
- Update patch with latest changes from master
- Update patch title and description
---
kernel/trace/trace_benchmark.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
index 811b08439406..e19c32f2a938 100644
--- a/kernel/trace/trace_benchmark.c
+++ b/kernel/trace/trace_benchmark.c
@@ -104,7 +104,7 @@ static void trace_do_benchmark(void)
stddev = 0;
delta = bm_total;
- delta = div64_u64(delta, bm_cnt);
+ do_div(delta, (u32)bm_cnt);
avg = delta;
if (stddev > 0) {
--
2.44.0© 2016 - 2026 Red Hat, Inc.