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From: Jiayu Hu <jiayu.hu@intel.com>
To: yang_y_yi <yang_y_yi@163.com>
Cc: jiayu.hu@intel.com, dev@dpdk.org, thomas@monjalon.net,
	yangyi01@inspur.com
Subject: Re: [dpdk-dev] [PATCH v6 2/3] gro: add VXLAN UDP/IPv4 GRO support
Date: Tue, 22 Sep 2020 14:55:46 +0800
Message-ID: <20200922065546.GA56452@NPG_DPDK_VIRTIO_jiayuhu_15.sh.intel.com> (raw)
In-Reply-To: <75421977.3967.174b47b6259.Coremail.yang_y_yi@163.com>

On Tue, Sep 22, 2020 at 02:23:39PM +0800, yang_y_yi wrote:
> Not a question, in next flush, they will be flushed, we have to check timestamp
> in the first time unless we don't strictly follow this time limitation.

who will check the timestamp? I did't get the point.

IMO, this will cause inconsistency of the rte_gro_timeout_flush().
BTW, what stops you to traverse all items and check timestamp
before flush them out?

> 
> At 2020-09-22 14:14:00, "Hu, Jiayu" <jiayu.hu@intel.com> wrote:
> 
>     Fragments of a flow are sorted by frag_oft, but they may have different
> 
>     timestamp. For example, there are three fragments, whose frag_oft is:
> 
>     frag[0].frag_oft=0, frag[1].frag_oft=4, frag[2].frag_oft=6; and they are
> 
>     fragments of one UDP packet but are not neighbors. In the first RX burst,
> 
>     host receives frag[1] and calls rte_gro_reassemble(), and we assume the
> 
>     timestamp of frag[1] is 10; in the second RX burst, host receives frag[0]
> 
>     and also call rte_gro_reassemble(), and timestamp of frag[0] is 11; the
> 
>     third time, host receives frag[2] and timestamp of frag[2] is 12. The three
> 
>     fragments are stored in three items of a UDP GRO table:
> 
>     items[0]: frag[0], timestamp is 11
> 
>     items[1]: frag[1], timestamp is 10
> 
>     items[2]: frag[2], timestamp is 12
> 
>     Now we want to flush packets whose timestamp is less than or equal to
> 
>     10. frag[1] should be returned, but in your code, no packets will be
>     flushed.
> 
>     Because the timestamp of items[0] is greater than 10, the left two
>     fragments
> 
>     will not be checked. This is what I want to say.
> 
>      
> 
>     From: yang_y_yi <yang_y_yi@163.com>
>     Sent: Tuesday, September 22, 2020 9:44 AM
>     To: Hu, Jiayu <jiayu.hu@intel.com>
>     Cc: dev@dpdk.org; thomas@monjalon.net; yangyi01@inspur.com
>     Subject: Re:Re: [dpdk-dev] [PATCH v6 2/3] gro: add VXLAN UDP/IPv4 GRO
>     support
>     Importance: High
> 
>      
> 
>     BTW, start_time is checked for the first packet in a flow,
>     gro_udp4_merge_items(tbl, j) will merge all the packets in this flow once
>     if they can be reassembled, gro_udp4_merge_items(tbl, j) doesn't check
>     start_time, so this still can let some new items in this flow have chance
>     to be merged.
> 
>     At 2020-09-22 09:29:38, "yang_y_yi" <yang_y_yi@163.com> wrote:
> 
>     >Thanks Jiayu, I have fixed other comments except this one:
> 
>     > 
> 
>     > 
> 
>     > 
> 
>     >>The items of a flow are ordered by frag_oft, and start_time
> 
>     >>of these items is not always in ascending order. Therefore,
> 
>     >>you cannot skip checking the items after the item whose
> 
>     >>start_time is greater than flush_timestamp. This issue also
> 
>     >>exists in UDP/IPv4 GRO, and need to correct them both.
> 
>     > 
> 
>     > 
> 
>     >I think the issue here is if we should strictly follow flush_timestamp, it is possible there are new items in items chain. we have chance to merge more packets if we don't follow flush_timestamp. So an ideal change can be this. But is it acceptible if we don't use flush_timestamp? It can flush some packets in advance therefore miss next merge window. Maybe current way is most resonable and a tradeoff between two exterem cases.
> 
>     > 
> 
>     > 
> 
>     > 
> 
>     > 
> 
>     > 
> 
>     >diff --git a/lib/librte_gro/gro_udp4.c b/lib/librte_gro/gro_udp4.c
> 
>     >index 061e7b0..ffa35a2 100644
> 
>     >--- a/lib/librte_gro/gro_udp4.c
> 
>     >+++ b/lib/librte_gro/gro_udp4.c
> 
>     >@@ -391,7 +391,6 @@
> 
>     > 
> 
>     >                j = tbl->flows[i].start_index;
> 
>     >                while (j != INVALID_ARRAY_INDEX) {
> 
>     >-                       if (tbl->items[j].start_time <= flush_timestamp) {
> 
>     >                                gro_udp4_merge_items(tbl, j);
> 
>     >                                out[k++] = tbl->items[j].firstseg;
> 
>     >                                if (tbl->items[j].nb_merged > 1)
> 
>     >@@ -407,12 +406,6 @@
> 
>     > 
> 
>     >                                if (unlikely(k == nb_out))
> 
>     >                                        return k;
> 
>     >-                       } else
> 
>     >-                               /*
> 
>     >-                                * The left packets in this flow won't be
> 
>     >-                                * timeout. Go to check other flows.
> 
>     >-                                */
> 
>     >-                               break;
> 
>     >                }
> 
>     >        }
> 
>     >        return k;
> 
>     > 
> 
>      
> 
> 
> 
>  
> 

  reply	other threads:[~2020-09-22  6:46 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-17  3:49 [dpdk-dev] [PATCH v6 0/3] gro: add UDP/IPv4 GRO and " yang_y_yi
2020-09-17  3:49 ` [dpdk-dev] [PATCH v6 1/3] gro: add " yang_y_yi
2020-09-21  6:21   ` Hu, Jiayu
2020-09-17  3:49 ` [dpdk-dev] [PATCH v6 2/3] gro: add VXLAN " yang_y_yi
2020-09-21  7:54   ` Hu, Jiayu
2020-09-22  1:29     ` yang_y_yi
2020-09-22  1:44       ` yang_y_yi
2020-09-22  6:14         ` Hu, Jiayu
2020-09-22  6:23           ` yang_y_yi
2020-09-22  6:55             ` Jiayu Hu [this message]
2020-09-22  7:38               ` yang_y_yi
2020-09-23  2:15                 ` Jiayu Hu
2020-09-23  2:28                   ` yang_y_yi
2020-09-23  2:43                     ` Jiayu Hu
2020-09-24  2:41                       ` yang_y_yi
2020-09-22  3:01       ` Jiayu Hu
2020-09-22  3:00         ` yang_y_yi
2020-09-17  3:49 ` [dpdk-dev] [PATCH v6 3/3] doc: update prog_guide and rel_notes for GRO yang_y_yi

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