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{
    "id": 35155,
    "url": "http://patches.dpdk.org/api/patches/35155/?format=api",
    "web_url": "http://patches.dpdk.org/project/dpdk/patch/B5748614-2B5F-402D-9A09-1C0781109000@mellanox.com/",
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        "id": 1,
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        "name": "DPDK",
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    "date": "2018-02-13T22:45:55",
    "name": "[dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()",
    "commit_ref": null,
    "pull_url": null,
    "state": "not-applicable",
    "archived": true,
    "hash": "56d940616436e6628c3851cf583a1e87bc3b6fe9",
    "submitter": {
        "id": 636,
        "url": "http://patches.dpdk.org/api/people/636/?format=api",
        "name": "Yongseok Koh",
        "email": "yskoh@mellanox.com"
    },
    "delegate": null,
    "mbox": "http://patches.dpdk.org/project/dpdk/patch/B5748614-2B5F-402D-9A09-1C0781109000@mellanox.com/mbox/",
    "series": [],
    "comments": "http://patches.dpdk.org/api/patches/35155/comments/",
    "check": "fail",
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    "tags": {},
    "related": [],
    "headers": {
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        "From": "Yongseok Koh <yskoh@mellanox.com>",
        "To": "Olivier Matz <olivier.matz@6wind.com>",
        "CC": "\"dev@dpdk.org\" <dev@dpdk.org>",
        "Thread-Topic": "Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()",
        "Thread-Index": "AQHTpRxoSpjpp7VOiUGxw51sLWTbeQ==",
        "Date": "Tue, 13 Feb 2018 22:45:55 +0000",
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        "Subject": "[dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()",
        "X-BeenThere": "dev@dpdk.org",
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        "List-Id": "DPDK patches and discussions <dev.dpdk.org>",
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        "Errors-To": "dev-bounces@dpdk.org",
        "Sender": "\"dev\" <dev-bounces@dpdk.org>"
    },
    "content": "Hi Olivier\n\nI'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of\nm->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems beneficial\nto the cases where almost mbufs have single segment.\n\nA customer reported high rate of cache misses in the code and I thought the\nfollowing patch could be helpful. I haven't had them try it yet but just wanted\nto hear from you.\n\nI'd appreciate if you can review this idea.\n\n\nThanks,\nYongseok",
    "diff": "diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h\nindex 62740254d..96edbcb9e 100644\n--- a/lib/librte_mbuf/rte_mbuf.h\n+++ b/lib/librte_mbuf/rte_mbuf.h\n@@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)\n                if (RTE_MBUF_INDIRECT(m))\n                        rte_pktmbuf_detach(m);\n \n-               if (m->next != NULL) {\n+               if (m->nb_segs > 1) {\n                        m->next = NULL;\n                        m->nb_segs = 1;\n                }\n@@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)\n                if (RTE_MBUF_INDIRECT(m))\n                        rte_pktmbuf_detach(m);\n \n-               if (m->next != NULL) {\n+               if (m->nb_segs > 1) {\n                        m->next = NULL;\n                        m->nb_segs = 1;\n                }\n",
    "prefixes": [
        "dpdk-dev"
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}