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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: d32e4e79-7aaa-4c66-98bb-08d7ec5d968b X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Apr 2020 16:51:39.6640 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: BnLgUtnjLooyIjPy+sQRb9ykyFG7o65WWeFy6J6Ka+/Uhse/yKcVpdtQRXP775AhipIf+zwFv7FtghPlQVbyxFkf2YSMWb2oAvVsvI+Y1y0= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR11MB2775 X-OriginatorOrg: intel.com Subject: Re: [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: stable-bounces@dpdk.org Sender: "stable" > -----Original Message----- > From: Phil Yang > Sent: Thursday, April 23, 2020 5:31 PM > To: Van Haaren, Harry ; dev@dpdk.org > Cc: thomas@monjalon.net; david.marchand@redhat.com; Ananyev, Konstantin > ; jerinj@marvell.com; > hemant.agrawal@nxp.com; Honnappa.Nagarahalli@arm.com; > gavin.hu@arm.com; nd@arm.com; Honnappa Nagarahalli > ; stable@dpdk.org > Subject: [PATCH v2 1/6] service: fix race condition for MT unsafe service >=20 > From: Honnappa Nagarahalli >=20 > The MT unsafe service might get configured to run on another core > while the service is running currently. This might result in the > MT unsafe service running on multiple cores simultaneously. Use > 'execute_lock' always when the service is MT unsafe. >=20 > Fixes: e9139a32f6e8 ("service: add function to run on app lcore") > Cc: stable@dpdk.org >=20 > Signed-off-by: Honnappa Nagarahalli > Reviewed-by: Phil Yang > --- Thanks for spinning a new revision - based on ML discussion previously, it seems like the "use service-run-count" to avoid this race would be a complex solution. Suggesting the following; 1) Take the approach as per this patch, to always take the atomic, fixing t= he race condition. 2) Add an API to service-cores, which allows "committing" of mappings. Comm= itting the mapping would imply that the mappings will not be changed in fut= ure. With runtime-remapping being removed from the equation, the existing b= ranch-over-atomic optimization is valid again. So this would offer applications two situations A) No application change: possible performance regression due to atomic alw= ays taken. B) Call "commit" API, and regain the performance as per previous DPDK versi= ons. Thoughts/opinions on the above? I've flagged the rest of the patchset for = review ASAP. Regards, -Harry > lib/librte_eal/common/rte_service.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) >=20 > diff --git a/lib/librte_eal/common/rte_service.c > b/lib/librte_eal/common/rte_service.c > index 70d17a5..b8c465e 100644 > --- a/lib/librte_eal/common/rte_service.c > +++ b/lib/librte_eal/common/rte_service.c > @@ -50,6 +50,10 @@ struct rte_service_spec_impl { > uint8_t internal_flags; >=20 > /* per service statistics */ > + /* Indicates how many cores the service is mapped to run on. > + * It does not indicate the number of cores the service is running > + * on currently. > + */ > rte_atomic32_t num_mapped_cores; > uint64_t calls; > uint64_t cycles_spent; > @@ -370,12 +374,7 @@ service_run(uint32_t i, struct core_state *cs, uint6= 4_t > service_mask, >=20 > cs->service_active_on_lcore[i] =3D 1; >=20 > - /* check do we need cmpset, if MT safe or <=3D 1 core > - * mapped, atomic ops are not required. > - */ > - const int use_atomics =3D (service_mt_safe(s) =3D=3D 0) && > - (rte_atomic32_read(&s->num_mapped_cores) > 1); > - if (use_atomics) { > + if (service_mt_safe(s) =3D=3D 0) { > if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1)) > return -EBUSY; >=20 > -- > 2.7.4