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Miller" , Jakub Kicinski , Tonghao Zhang , netdev , dev@openvswitch.org, Linux Kernel Mailing List Subject: Re: [PATCH] net: openvswitch: use do_div() for 64-by-32 divisions: In-Reply-To: References: <20200424121051.5056-1-geert@linux-m68k.org> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 24 Apr 2020 18:45:47 +0200 Message-ID: <87ftcs3k90.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Geert Uytterhoeven writes: > Hi Eric, > > On Fri, Apr 24, 2020 at 5:05 PM Eric Dumazet wrote: >> On 4/24/20 5:10 AM, Geert Uytterhoeven wrote: >> > On 32-bit architectures (e.g. m68k): >> > >> > ERROR: modpost: "__udivdi3" [net/openvswitch/openvswitch.ko] undefined! >> > ERROR: modpost: "__divdi3" [net/openvswitch/openvswitch.ko] undefined! >> > >> > Fixes: e57358873bb5d6ca ("net: openvswitch: use u64 for meter bucket") >> > Reported-by: noreply@ellerman.id.au >> > Signed-off-by: Geert Uytterhoeven >> > --- >> > net/openvswitch/meter.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c >> > index 915f31123f235c03..3498a5ab092ab2b8 100644 >> > --- a/net/openvswitch/meter.c >> > +++ b/net/openvswitch/meter.c >> > @@ -393,7 +393,7 @@ static struct dp_meter *dp_meter_create(struct nlattr **a) >> > * Start with a full bucket. >> > */ >> > band->bucket = (band->burst_size + band->rate) * 1000ULL; >> > - band_max_delta_t = band->bucket / band->rate; >> > + band_max_delta_t = do_div(band->bucket, band->rate); >> > if (band_max_delta_t > meter->max_delta_t) >> > meter->max_delta_t = band_max_delta_t; >> > band++; >> > >> >> This is fascinating... Have you tested this patch ? > > Sorry, I should have said this is compile-tested only. > >> Please double check what do_div() return value is supposed to be ! > > I do not have any openvswitch setups, let alone on the poor m68k box. I think what Eric is referring to is this, from the documentation of do_div: * do_div - returns 2 values: calculate remainder and update new dividend * @n: uint64_t dividend (will be updated) * @base: uint32_t divisor * * Summary: * ``uint32_t remainder = n % base;`` * ``n = n / base;`` * * Return: (uint32_t)remainder Specifically that last part :) -Toke