Re: [dpdk-dev] [PATCH v9 2/3] test/atomic: add 128b compare and swap test

["Phil Yang (Arm Technology China)" <Phil.Yang@arm.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Monday, October 14, 2019 11:45 PM
> To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>
> Cc: thomas@monjalon.net; jerinj@marvell.com; Gage Eads
> <gage.eads@intel.com>; dev <dev@dpdk.org>; hemant.agrawal@nxp.com;
> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm
> Technology China) <Gavin.Hu@arm.com>; nd <nd@arm.com>
> Subject: Re: [dpdk-dev] [PATCH v9 2/3] test/atomic: add 128b compare and
> swap test
> 
> On Wed, Aug 14, 2019 at 10:29 AM Phil Yang <phil.yang@arm.com> wrote:
> >
> > Add 128b atomic compare and swap test for aarch64 and x86_64.
> >
> > Signed-off-by: Phil Yang <phil.yang@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Acked-by: Gage Eads <gage.eads@intel.com>
> > Acked-by: Jerin Jacob <jerinj@marvell.com>
> > Tested-by: Jerin Jacob <jerinj@marvell.com>
> > ---
> >  app/test/test_atomic.c | 125
> ++++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 123 insertions(+), 2 deletions(-)
> >
> > diff --git a/app/test/test_atomic.c b/app/test/test_atomic.c
> > index 43be30e..0dad923 100644
> > --- a/app/test/test_atomic.c
> > +++ b/app/test/test_atomic.c
> > @@ -1,5 +1,6 @@
> >  /* SPDX-License-Identifier: BSD-3-Clause
> >   * Copyright(c) 2010-2014 Intel Corporation
> > + * Copyright(c) 2019 Arm Limited
> >   */
> >
> >  #include <stdio.h>
> > @@ -20,7 +21,7 @@
> >   * Atomic Variables
> >   * ================
> >   *
> > - * - The main test function performs three subtests. The first test
> > + * - The main test function performs four subtests. The first test
> >   *   checks that the usual inc/dec/add/sub functions are working
> >   *   correctly:
> >   *
> > @@ -61,11 +62,27 @@
> >   *       atomic_sub(&count, tmp+1);
> >   *
> >   *   - At the end of the test, the *count* value must be 0.
> > + *
> > + * - Test "128b compare and swap" (aarch64 and x86_64 only)
> > + *
> > + *   - Initialize 128-bit atomic variables to zero.
> > + *
> > + *   - Invoke ``test_atomici128_cmp_exchange()`` on each lcore. Before
> doing
> 
> Typo, atomic128.

Updated in v10.

> 
> 
> > + *     anything else, the cores are waiting a synchro. Each lcore does
> > + *     these compare and swap (CAS) operations several times::
> > + *
> > + *       Acquired CAS update counter.val[0] + 2; counter.val[1] + 1;
> > + *       Released CAS update counter.val[0] + 2; counter.val[1] + 1;
> > + *       Acquired_Released CAS update counter.val[0] + 2; counter.val[1] + 1;
> > + *       Relaxed CAS update counter.val[0] + 2; counter.val[1] + 1;
> > + *
> > + *   - At the end of the test, the *count128* first 64-bit value and
> > + *     second 64-bit value differ by the total iterations.
> >   */
> >
> >  #define NUM_ATOMIC_TYPES 3
> >
> > -#define N 10000
> > +#define N 1000000
> 
> This change the number of iterations for this test.
> Did you evaluate the impact on the test duration?
> I suppose this is fairly quick, but could you explain why this has
> been extended?

By extending the iterations to 1 million times it can test the stability of these atomic APIs, 
especial for the new added 128bit atomics. 
Yes, I did the evaluation. It has no impact on the test duration as the test case is simple.

> The commitlog does not give hints.
Thanks for pointing out this. I have updated this in the v10 commitlog.
 
> 
> 
> >
> >  static rte_atomic16_t a16;
> >  static rte_atomic32_t a32;
> > @@ -216,6 +233,78 @@
> test_atomic_dec_and_test(__attribute__((unused)) void *arg)
> >         return 0;
> >  }
> >
> > +#if defined(RTE_ARCH_X86_64) || defined(RTE_ARCH_ARM64)
> > +static rte_int128_t count128;
> > +
> > +/*
> > + * rte_atomic128_cmp_exchange() should update a 128 bits counter's first
> 64
> > + * bits by 2 and the second 64 bits by 1 in this test. It should return true
> > + * if the compare exchange operation is successful.
> > + * This test repeats 128 bits compare and swap operations 10K rounds. In
> each
> 
> s/10K/N/

Updated in v10.

<snip>

> > +#if defined(RTE_ARCH_X86_64) || defined(RTE_ARCH_ARM64)
> > +       /*
> > +        * This case tests the functionality of rte_atomic128b_cmp_exchange
> > +        * API. It calls rte_atomic128b_cmp_exchange with four kinds of
> memory
> > +        * models successively on each slave core. Once each 128-bit atomic
> > +        * compare and swap operation is successful, it updates the global
> > +        * 128-bit counter by 2 for the first 64-bit and 1 for the second
> > +        * 64-bit. Each slave core iterates this test 10K times.
> 
> N times.

Updated in v10.

Thanks,
Phil

> 
> 
> > +        * At the end of test, verify whether the first 64-bits of the 128-bit
> > +        * counter and the second 64bits is differ by the total iterations. If
> > +        * it is, the test passes.
> > +        */
> > +       printf("128b compare and swap test\n");
> > +       uint64_t iterations = 0;
> > +
> > +       rte_atomic32_clear(&synchro);
> > +       count128.val[0] = 0;
> > +       count128.val[1] = 0;
> > +
> > +       rte_eal_mp_remote_launch(test_atomic128_cmp_exchange, NULL,
> > +                                SKIP_MASTER);
> > +       rte_atomic32_set(&synchro, 1);
> > +       rte_eal_mp_wait_lcore();
> > +       rte_atomic32_clear(&synchro);
> > +
> > +       iterations = count128.val[0] - count128.val[1];
> > +       if (iterations != 4*N*(rte_lcore_count()-1)) {
> > +               printf("128b compare and swap failed\n");
> > +               return -1;
> > +       }
> > +#endif
> > +
> >         return 0;
> >  }
> >
> > --
> > 2.7.4
> >
> 
> 
> --
> David Marchand