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{
    "id": 73458,
    "url": "https://patches.dpdk.org/api/patches/73458/?format=api",
    "web_url": "https://patches.dpdk.org/patch/73458/",
    "project": {
        "id": 1,
        "url": "https://patches.dpdk.org/api/projects/1/?format=api",
        "name": "DPDK",
        "link_name": "dpdk",
        "list_id": "dev.dpdk.org",
        "list_email": "dev@dpdk.org",
        "web_url": "http://core.dpdk.org",
        "scm_url": "git://dpdk.org/dpdk",
        "webscm_url": "http://git.dpdk.org/dpdk"
    },
    "msgid": "<1594137293-22468-2-git-send-email-phil.yang@arm.com>",
    "date": "2020-07-07T15:54:51",
    "name": "[v4,2/4] eventdev: use C11 atomics for lcore timer armed flag",
    "commit_ref": null,
    "pull_url": null,
    "state": "accepted",
    "archived": true,
    "hash": "3962afa3c13ffaf3688782e10977350a28f497c3",
    "submitter": {
        "id": 833,
        "url": "https://patches.dpdk.org/api/people/833/?format=api",
        "name": "Phil Yang",
        "email": "phil.yang@arm.com"
    },
    "delegate": {
        "id": 310,
        "url": "https://patches.dpdk.org/api/users/310/?format=api",
        "username": "jerin",
        "first_name": "Jerin",
        "last_name": "Jacob",
        "email": "jerin.jacob@caviumnetworks.com"
    },
    "mbox": "https://patches.dpdk.org/patch/73458/mbox/",
    "series": [
        {
            "id": 10861,
            "url": "https://patches.dpdk.org/api/series/10861/?format=api",
            "web_url": "https://patches.dpdk.org/project/dpdk/list/?series=10861",
            "date": "2020-07-07T15:54:50",
            "name": "[v4,1/4] eventdev: fix race condition on timer list counter",
            "version": 4,
            "mbox": "https://patches.dpdk.org/series/10861/mbox/"
        }
    ],
    "comments": "https://patches.dpdk.org/api/patches/73458/comments/",
    "check": "fail",
    "checks": "https://patches.dpdk.org/api/patches/73458/checks/",
    "tags": {},
    "headers": {
        "List-Subscribe": "<https://mails.dpdk.org/listinfo/dev>,\n <mailto:dev-request@dpdk.org?subject=subscribe>",
        "X-Mailman-Version": "2.1.15",
        "Precedence": "list",
        "X-Original-To": "patchwork@inbox.dpdk.org",
        "List-Post": "<mailto:dev@dpdk.org>",
        "References": "<1594120403-17643-1-git-send-email-phil.yang@arm.com>\n <1594137293-22468-1-git-send-email-phil.yang@arm.com>",
        "X-BeenThere": "dev@dpdk.org",
        "List-Id": "DPDK patches and discussions <dev.dpdk.org>",
        "Subject": "[dpdk-dev] [PATCH v4 2/4] eventdev: use C11 atomics for lcore timer\n\tarmed flag",
        "Sender": "\"dev\" <dev-bounces@dpdk.org>",
        "From": "Phil Yang <phil.yang@arm.com>",
        "Received": [
            "from dpdk.org (dpdk.org [92.243.14.124])\n\tby inbox.dpdk.org (Postfix) with ESMTP id 20827A00BE;\n\tTue,  7 Jul 2020 17:55:32 +0200 (CEST)",
            "from [92.243.14.124] (localhost [127.0.0.1])\n\tby dpdk.org (Postfix) with ESMTP id 76D2A1DEB8;\n\tTue,  7 Jul 2020 17:55:25 +0200 (CEST)",
            "from foss.arm.com (foss.arm.com [217.140.110.172])\n by dpdk.org (Postfix) with ESMTP id F22A11DEB3;\n Tue,  7 Jul 2020 17:55:23 +0200 (CEST)",
            "from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14])\n by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 72041D6E;\n Tue,  7 Jul 2020 08:55:23 -0700 (PDT)",
            "from phil-VirtualBox.arm.com (A010647.Arm.com [10.170.226.105])\n by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 2CBFB3F68F;\n Tue,  7 Jul 2020 08:55:18 -0700 (PDT)"
        ],
        "To": "jerinj@marvell.com,\n\tdev@dpdk.org",
        "X-Mailer": "git-send-email 2.7.4",
        "List-Unsubscribe": "<https://mails.dpdk.org/options/dev>,\n <mailto:dev-request@dpdk.org?subject=unsubscribe>",
        "Date": "Tue,  7 Jul 2020 23:54:51 +0800",
        "List-Archive": "<http://mails.dpdk.org/archives/dev/>",
        "Delivered-To": "patchwork@inbox.dpdk.org",
        "In-Reply-To": "<1594137293-22468-1-git-send-email-phil.yang@arm.com>",
        "Cc": "thomas@monjalon.net, erik.g.carrillo@intel.com,\n Honnappa.Nagarahalli@arm.com, drc@linux.vnet.ibm.com, Ruifeng.Wang@arm.com,\n Dharmik.Thakkar@arm.com, nd@arm.com, david.marchand@redhat.com,\n mdr@ashroe.eu, nhorman@tuxdriver.com, dodji@redhat.com, stable@dpdk.org",
        "List-Help": "<mailto:dev-request@dpdk.org?subject=help>",
        "Errors-To": "dev-bounces@dpdk.org",
        "Message-Id": "<1594137293-22468-2-git-send-email-phil.yang@arm.com>",
        "Return-Path": "<dev-bounces@dpdk.org>"
    },
    "content": "The in_use flag is a per core variable which is not shared between\nlcores in the normal case and the access of this variable should be\nordered on the same core. However, if non-EAL thread pick the highest\nlcore to insert timers into, there is the possibility of conflicts\non this flag between threads. Then the atomic compare-and-swap\noperation is needed.\n\nUse the C11 atomics instead of the generic rte_atomic operations to\navoid the unnecessary barrier on aarch64.\n\nCc: stable@dpdk.org\n\nSigned-off-by: Phil Yang <phil.yang@arm.com>\nReviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>\nReviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>\nAcked-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>\n---\nv4:\n1.Change 'CAS' to 'compare-and-swap' to pass the coding style check.\n2.Cc to stable release. (Honnappa)\n\nv2:\n1. Make the code comments more accurate. (Erik)\n2. Define the in_use flag as an unsigned type. (Stephen)\n\n lib/librte_eventdev/rte_event_timer_adapter.c | 15 +++++++++++----\n 1 file changed, 11 insertions(+), 4 deletions(-)",
    "diff": "diff --git a/lib/librte_eventdev/rte_event_timer_adapter.c b/lib/librte_eventdev/rte_event_timer_adapter.c\nindex 370ea40..4ed3013 100644\n--- a/lib/librte_eventdev/rte_event_timer_adapter.c\n+++ b/lib/librte_eventdev/rte_event_timer_adapter.c\n@@ -554,7 +554,7 @@ struct swtim {\n \tuint32_t timer_data_id;\n \t/* Track which cores have actually armed a timer */\n \tstruct {\n-\t\trte_atomic16_t v;\n+\t\tuint16_t v;\n \t} __rte_cache_aligned in_use[RTE_MAX_LCORE];\n \t/* Track which cores' timer lists should be polled */\n \tunsigned int poll_lcores[RTE_MAX_LCORE];\n@@ -606,7 +606,8 @@ swtim_callback(struct rte_timer *tim)\n \t\t\t\t      \"with immediate expiry value\");\n \t\t}\n \n-\t\tif (unlikely(rte_atomic16_test_and_set(&sw->in_use[lcore].v))) {\n+\t\tif (unlikely(sw->in_use[lcore].v == 0)) {\n+\t\t\tsw->in_use[lcore].v = 1;\n \t\t\tn_lcores = __atomic_fetch_add(&sw->n_poll_lcores, 1,\n \t\t\t\t\t\t     __ATOMIC_RELAXED);\n \t\t\t__atomic_store_n(&sw->poll_lcores[n_lcores], lcore,\n@@ -834,7 +835,7 @@ swtim_init(struct rte_event_timer_adapter *adapter)\n \n \t/* Initialize the variables that track in-use timer lists */\n \tfor (i = 0; i < RTE_MAX_LCORE; i++)\n-\t\trte_atomic16_init(&sw->in_use[i].v);\n+\t\tsw->in_use[i].v = 0;\n \n \t/* Initialize the timer subsystem and allocate timer data instance */\n \tret = rte_timer_subsystem_init();\n@@ -1017,6 +1018,8 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,\n \tstruct rte_timer *tim, *tims[nb_evtims];\n \tuint64_t cycles;\n \tint n_lcores;\n+\t/* Timer list for this lcore is not in use. */\n+\tuint16_t exp_state = 0;\n \n #ifdef RTE_LIBRTE_EVENTDEV_DEBUG\n \t/* Check that the service is running. */\n@@ -1035,8 +1038,12 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,\n \t/* If this is the first time we're arming an event timer on this lcore,\n \t * mark this lcore as \"in use\"; this will cause the service\n \t * function to process the timer list that corresponds to this lcore.\n+\t * The atomic compare-and-swap operation can prevent the race condition\n+\t * on in_use flag between multiple non-EAL threads.\n \t */\n-\tif (unlikely(rte_atomic16_test_and_set(&sw->in_use[lcore_id].v))) {\n+\tif (unlikely(__atomic_compare_exchange_n(&sw->in_use[lcore_id].v,\n+\t\t\t&exp_state, 1, 0,\n+\t\t\t__ATOMIC_RELAXED, __ATOMIC_RELAXED))) {\n \t\tEVTIM_LOG_DBG(\"Adding lcore id = %u to list of lcores to poll\",\n \t\t\t      lcore_id);\n \t\tn_lcores = __atomic_fetch_add(&sw->n_poll_lcores, 1,\n",
    "prefixes": [
        "v4",
        "2/4"
    ]
}