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{
    "id": 15587,
    "url": "http://patches.dpdk.org/api/patches/15587/?format=api",
    "web_url": "http://patches.dpdk.org/project/dpdk/patch/1472793906-5699-1-git-send-email-slayercat.subscription@gmail.com/",
    "project": {
        "id": 1,
        "url": "http://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",
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    "msgid": "<1472793906-5699-1-git-send-email-slayercat.subscription@gmail.com>",
    "list_archive_url": "https://inbox.dpdk.org/dev/1472793906-5699-1-git-send-email-slayercat.subscription@gmail.com",
    "date": "2016-09-02T05:25:06",
    "name": "[dpdk-dev] mbuf: fix atomic refcnt update synchronization",
    "commit_ref": null,
    "pull_url": null,
    "state": "rejected",
    "archived": true,
    "hash": "f87167e50cd41da43cb34c08d1ad4a60c664ffe1",
    "submitter": {
        "id": 554,
        "url": "http://patches.dpdk.org/api/people/554/?format=api",
        "name": "lilinzhe",
        "email": "slayercat.subscription@gmail.com"
    },
    "delegate": {
        "id": 1,
        "url": "http://patches.dpdk.org/api/users/1/?format=api",
        "username": "tmonjalo",
        "first_name": "Thomas",
        "last_name": "Monjalon",
        "email": "thomas@monjalon.net"
    },
    "mbox": "http://patches.dpdk.org/project/dpdk/patch/1472793906-5699-1-git-send-email-slayercat.subscription@gmail.com/mbox/",
    "series": [],
    "comments": "http://patches.dpdk.org/api/patches/15587/comments/",
    "check": "pending",
    "checks": "http://patches.dpdk.org/api/patches/15587/checks/",
    "tags": {},
    "related": [],
    "headers": {
        "Return-Path": "<dev-bounces@dpdk.org>",
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        "From": "lilinzhe <slayercat.subscription@gmail.com>",
        "To": "dev@dpdk.org",
        "Cc": "=?UTF-8?q?=E6=9D=8E=E6=9E=97=E5=93=B2?= <lilinzhe@ijinshan.com>",
        "Date": "Fri,  2 Sep 2016 13:25:06 +0800",
        "Message-Id": "<1472793906-5699-1-git-send-email-slayercat.subscription@gmail.com>",
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        "MIME-Version": "1.0",
        "Content-Type": "text/plain; charset=UTF-8",
        "Content-Transfer-Encoding": "8bit",
        "Subject": "[dpdk-dev] [PATCH] mbuf: fix atomic refcnt update synchronization",
        "X-BeenThere": "dev@dpdk.org",
        "X-Mailman-Version": "2.1.15",
        "Precedence": "list",
        "List-Id": "patches and discussions about DPDK <dev.dpdk.org>",
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    },
    "content": "From: 李林哲 <lilinzhe@ijinshan.com>\n\nchagne atomic ref update to always call atomic_add\n\nwhen mbuf is allocated by cpu1 and freed by cpu2. cpu1 cache may not be updated by such a set operation.\ncauses refcnt reads incorrect values.\n---\n lib/librte_mbuf/rte_mbuf.h | 16 ++++++----------\n 1 file changed, 6 insertions(+), 10 deletions(-)",
    "diff": "diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h\nindex 7ea66ed..63e6588 100644\n--- a/lib/librte_mbuf/rte_mbuf.h\n+++ b/lib/librte_mbuf/rte_mbuf.h\n@@ -786,7 +786,7 @@ struct rte_mbuf {\n \t */\n \tunion {\n \t\trte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */\n-\t\tuint16_t refcnt;              /**< Non-atomically accessed refcnt */\n+\t\tvolatile uint16_t refcnt;     /**< Non-atomically accessed refcnt */\n \t};\n \tuint8_t nb_segs;          /**< Number of segments. */\n \tuint8_t port;             /**< Input port. */\n@@ -1060,16 +1060,12 @@ static inline uint16_t\n rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)\n {\n \t/*\n-\t * The atomic_add is an expensive operation, so we don't want to\n-\t * call it in the case where we know we are the uniq holder of\n-\t * this mbuf (i.e. ref_cnt == 1). Otherwise, an atomic\n-\t * operation has to be used because concurrent accesses on the\n-\t * reference counter can occur.\n+\t * This shell always call atomic_add\n+\t *\n+\t * when mbuf is allocated by cpu1 and freed by cpu2. cpu1 cache may not be updated by such a set operation.\n+\t * causes refcnt reads incorrect values\n+\t * \n \t */\n-\tif (likely(rte_mbuf_refcnt_read(m) == 1)) {\n-\t\trte_mbuf_refcnt_set(m, 1 + value);\n-\t\treturn 1 + value;\n-\t}\n \n \treturn (uint16_t)(rte_atomic16_add_return(&m->refcnt_atomic, value));\n }\n",
    "prefixes": [
        "dpdk-dev"
    ]
}