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SubjectRe: [PATCH] ipvs: use div_s64 for signed division

Hello,

On Thu, 15 Dec 2022, Arnd Bergmann wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> do_div() is only well-behaved for positive numbers, and now warns
> when the first argument is a an s64:
>
> net/netfilter/ipvs/ip_vs_est.c: In function 'ip_vs_est_calc_limits':
> include/asm-generic/div64.h:222:35: error: comparison of distinct pointer types lacks a cast [-Werror]
> 222 | (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
> | ^~
> net/netfilter/ipvs/ip_vs_est.c:694:17: note: in expansion of macro 'do_div'
> 694 | do_div(val, loops);

net-next already contains fix for this warning
and changes val to u64.

> Convert to using the more appropriate div_s64(), which also
> simplifies the code a bit.
>
> Fixes: 705dd3444081 ("ipvs: use kthreads for stats estimation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> net/netfilter/ipvs/ip_vs_est.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_est.c b/net/netfilter/ipvs/ip_vs_est.c
> index ce2a1549b304..dbc32f8cf1f9 100644
> --- a/net/netfilter/ipvs/ip_vs_est.c
> +++ b/net/netfilter/ipvs/ip_vs_est.c
> @@ -691,15 +691,13 @@ static int ip_vs_est_calc_limits(struct netns_ipvs *ipvs, int *chain_max)
> }
> if (diff >= NSEC_PER_SEC)
> continue;
> - val = diff;
> - do_div(val, loops);
> + val = div_s64(diff, loops);

On CONFIG_X86_32 both versions execute single divl
for our case but div_s64 is not inlined. I'm not expert in
this area but if you think div_u64 is more appropriate then
post another patch. Note that now val is u64 and
min_est is still s32 (can be u32).

> if (!min_est || val < min_est) {
> min_est = val;
> /* goal: 95usec per chain */
> val = 95 * NSEC_PER_USEC;
> if (val >= min_est) {
> - do_div(val, min_est);
> - max = (int)val;
> + max = div_s64(val, min_est);
> } else {
> max = 1;
> }
> --
> 2.35.1

Regards

--
Julian Anastasov <ja@ssi.bg>

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