From: Pavan Nikhilesh <pbhagavatula@marvell.com> Fix off by one error in 64bit reciprocal division when divisor is 32bit. Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide") Cc: stable@dpdk.org Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com> --- Example: Division failed, 17358247066007716387/244 = expected 71140356827900476 result 71140356827900477 Division failed, 17541123788887206374/41475 = expected 422932460250444 result 422932460250445 lib/librte_eal/common/rte_reciprocal.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c index f017d0c28..1c6d10e73 100644 --- a/lib/librte_eal/common/rte_reciprocal.c +++ b/lib/librte_eal/common/rte_reciprocal.c @@ -133,12 +133,15 @@ rte_reciprocal_value_u64(uint64_t d) { struct rte_reciprocal_u64 R; uint64_t m; + uint64_t r; int l; l = 63 - __builtin_clzll(d); - m = divide_128_div_64_to_64((1ULL << l), 0, d, NULL) << 1; - m = (1ULL << l) - d ? m + 2 : 1; + m = divide_128_div_64_to_64((1ULL << l), 0, d, &r) << 1; + if (r << 1 < r || r << 1 >= d) + m++; + m = (1ULL << l) - d ? m + 1 : 1; R.m = m; R.sh1 = l > 1 ? 1 : l; -- 2.23.0
On Tue, Sep 3, 2019 at 9:17 PM <pbhagavatula@marvell.com> wrote:
>
> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>
> Fix off by one error in 64bit reciprocal division when divisor is 32bit.
>
> Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide")
> Cc: stable@dpdk.org
>
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Any review?
Are we missing an update in the unit test to catch this issue?
Thanks.
--
David Marchand
>-----Original Message----- >From: David Marchand <david.marchand@redhat.com> >Sent: Tuesday, October 15, 2019 2:16 PM >To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Stephen >Hemminger <stephen@networkplumber.org> >Cc: dev <dev@dpdk.org>; Pavan Nikhilesh Bhagavatula ><pbhagavatula@marvell.com>; dpdk stable <stable@dpdk.org>; Aaron >Conole <aconole@redhat.com> >Subject: Re: [dpdk-dev] [PATCH] eal/reciprocal: fix off by one >when divisor is 32bit >On Tue, Sep 3, 2019 at 9:17 PM <pbhagavatula@marvell.com> wrote: >> >> From: Pavan Nikhilesh <pbhagavatula@marvell.com> >> >> Fix off by one error in 64bit reciprocal division when divisor is 32bit. >> >> Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide") >> Cc: stable@dpdk.org >> >> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com> > >Any review? > >Are we missing an update in the unit test to catch this issue? >Thanks. We actually caught it in a unit test >test_reciprocal_division > >-- >David Marchand
On Tue, Oct 15, 2019 at 10:56 AM Pavan Nikhilesh Bhagavatula
<pbhagavatula@marvell.com> wrote:
>
>
>
> >-----Original Message-----
> >From: David Marchand <david.marchand@redhat.com>
> >Sent: Tuesday, October 15, 2019 2:16 PM
> >To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Stephen
> >Hemminger <stephen@networkplumber.org>
> >Cc: dev <dev@dpdk.org>; Pavan Nikhilesh Bhagavatula
> ><pbhagavatula@marvell.com>; dpdk stable <stable@dpdk.org>; Aaron
> >Conole <aconole@redhat.com>
> >Subject: Re: [dpdk-dev] [PATCH] eal/reciprocal: fix off by one
> >when divisor is 32bit
> >On Tue, Sep 3, 2019 at 9:17 PM <pbhagavatula@marvell.com> wrote:
> >>
> >> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >>
> >> Fix off by one error in 64bit reciprocal division when divisor is 32bit.
> >>
> >> Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide")
> >> Cc: stable@dpdk.org
> >>
> >> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >
> >Any review?
> >
> >Are we missing an update in the unit test to catch this issue?
> >Thanks.
>
> We actually caught it in a unit test
> >test_reciprocal_division
We had this problem since the very start then.
Both reciprocal_division and reciprocal_division_perf are in the "perf" list.
Can they be promoted to the standard list?
--
David Marchand
>> > >> >Any review? >> > >> >Are we missing an update in the unit test to catch this issue? >> >Thanks. >> >> We actually caught it in a unit test >> >test_reciprocal_division > >We had this problem since the very start then. > >Both reciprocal_division and reciprocal_division_perf are in the "perf" >list. >Can they be promoted to the standard list? Both of these tests take >=5 min depending on the platform in use which is why they are placed in perf tests. > > >-- >David Marchand
Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: >>> > >>> >Any review? >>> > >>> >Are we missing an update in the unit test to catch this issue? >>> >Thanks. >>> >>> We actually caught it in a unit test >>> >test_reciprocal_division >> >>We had this problem since the very start then. >> >>Both reciprocal_division and reciprocal_division_perf are in the "perf" >>list. >>Can they be promoted to the standard list? > > Both of these tests take >=5 min depending on the platform in use which is why > they are placed in perf tests. Is it possible to write a smaller set of tests that can be put in the standard list? >> >> >>-- >>David Marchand
>Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: > >>>> > >>>> >Any review? >>>> > >>>> >Are we missing an update in the unit test to catch this issue? >>>> >Thanks. >>>> >>>> We actually caught it in a unit test >>>> >test_reciprocal_division >>> >>>We had this problem since the very start then. >>> >>>Both reciprocal_division and reciprocal_division_perf are in the >"perf" >>>list. >>>Can they be promoted to the standard list? >> >> Both of these tests take >=5 min depending on the platform in use >which is why >> they are placed in perf tests. > >Is it possible to write a smaller set of tests that can be put in the >standard list? > Currently we have MAX_ITERATIONS (1ULL << 32) for both the tests maybe we can reduce it to 1 << 16 for the normal case? >>> >>> >>>-- >>>David Marchand
Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: >>Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: >> >>>>> > >>>>> >Any review? >>>>> > >>>>> >Are we missing an update in the unit test to catch this issue? >>>>> >Thanks. >>>>> >>>>> We actually caught it in a unit test >>>>> >test_reciprocal_division >>>> >>>>We had this problem since the very start then. >>>> >>>>Both reciprocal_division and reciprocal_division_perf are in the >>"perf" >>>>list. >>>>Can they be promoted to the standard list? >>> >>> Both of these tests take >=5 min depending on the platform in use >>which is why >>> they are placed in perf tests. >> >>Is it possible to write a smaller set of tests that can be put in the >>standard list? >> > > Currently we have MAX_ITERATIONS (1ULL << 32) for both the tests > maybe we can reduce it to 1 << 16 for the normal case? Sounds good to me. If you submit a patch, we can look at the run time from the robot submission as well. >>>> >>>> >>>>-- >>>>David Marchand
>Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: > >>>Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> writes: >>> >>>>>> > >>>>>> >Any review? >>>>>> > >>>>>> >Are we missing an update in the unit test to catch this issue? >>>>>> >Thanks. >>>>>> >>>>>> We actually caught it in a unit test >>>>>> >test_reciprocal_division >>>>> >>>>>We had this problem since the very start then. >>>>> >>>>>Both reciprocal_division and reciprocal_division_perf are in the >>>"perf" >>>>>list. >>>>>Can they be promoted to the standard list? >>>> >>>> Both of these tests take >=5 min depending on the platform in use >>>which is why >>>> they are placed in perf tests. >>> >>>Is it possible to write a smaller set of tests that can be put in the >>>standard list? >>> >> >> Currently we have MAX_ITERATIONS (1ULL << 32) for both the tests >> maybe we can reduce it to 1 << 16 for the normal case? > >Sounds good to me. If you submit a patch, we can look at the run time >from the robot submission as well. > Yup, I'll send a patch. >>>>> >>>>> >>>>>-- >>>>>David Marchand
On Tue, Sep 3, 2019 at 9:17 PM <pbhagavatula@marvell.com> wrote: > > From: Pavan Nikhilesh <pbhagavatula@marvell.com> > > Fix off by one error in 64bit reciprocal division when divisor is 32bit. Added log from unit test: RTE>>reciprocal_division Validating unsigned 32bit division. Validating unsigned 64bit division. Validating unsigned 64bit division with 32bit divisor. Division failed, 16983222950483802557/819 = expected 20736535959076681 result 20736535959076682 Validating division by power of 2. Test Failed > > Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide") > Cc: stable@dpdk.org > > Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com> Please continue working on enhancing the functional test so that it can be part of the standard unit test list. Thanks. -- David Marchand