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Fri, 04 Jul 2025 07:57:09 -0400 X-MC-Unique: j2jYXpJcPQevP9VfK6bBZQ-1 X-Mimecast-MFC-AGG-ID: j2jYXpJcPQevP9VfK6bBZQ_1751630228 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3BA0618002ED; Fri, 4 Jul 2025 11:57:07 +0000 (UTC) Received: from [10.44.22.8] (unknown [10.44.22.8]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3D611180035C; Fri, 4 Jul 2025 11:57:03 +0000 (UTC) Message-ID: <7be991f8-a7d7-48c7-af5b-dad4aaacb486@redhat.com> Date: Fri, 4 Jul 2025 13:57:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] net/virtio: Fix check of threshold for Tx freeing To: "Jiang, YuX" , Hengqi Chen , "dev@dpdk.org" , Thomas Monjalon , David Marchand Cc: Baoyuan Li , Chenbo Xia References: <20250609072347.1748785-1-hengqi.chen@gmail.com> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Hi Yu, Hengqi, First, thanks Yu for testing and reporting the performance degradation, this is much appreciated! On 7/4/25 1:29 PM, Jiang, YuX wrote: > Hi Hengqi, > > Can you help to check the ticket: https://bugs.dpdk.org/show_bug.cgi?id=1747? The perf drop is caused by your patch. Thanks so much. The options I see are: 1. Revert the patch for v25.07, fix it and resubmit for v25.11. 2. Fix it on time for v25.07-rc3 3. Keep the patch in v25.07 and try to fix it in v25.11. As I will be OoO starting this evening, I would be in favor of option 1. What do you think? Thanks, Maxime > Best regards, > Yu Jiang > >> -----Original Message----- >> From: Hengqi Chen >> Sent: Monday, June 9, 2025 3:24 PM >> To: dev@dpdk.org >> Cc: Hengqi Chen ; Baoyuan Li >> ; Maxime Coquelin ; >> Chenbo Xia >> Subject: [PATCH] net/virtio: Fix check of threshold for Tx freeing >> >> Like most dirvers, make the fast path of virtio_xmit_cleanup() behave as >> described by the comments of rte_eth_txconf::tx_free_thresh ([0]): >> Start freeing Tx buffers if there are >> less free descriptors than this value. >> >> The rationale behind this change is that: >> * vq->vq_nentries is set during device probe with the queue size specified >> by vhost backend, this value does not reflect the real nb_tx_desc >> * the real available tx desc is set to vq->vq_free_cnt via the nb_tx_desc >> param of rte_eth_tx_queue_setup() API >> * so `nb_used > vq->vq_nentries - vq->vq_free_thresh` could never be true >> if say nb_tx_desc=2048, vq->vq_nentries=4096, vq->vq_free_thresh=32, >> see bug report 1716 ([1]) for details. >> >> Bugzilla ID: 1716 >> >> [0]: https://github.com/DPDK/dpdk/commit/72514b5d5543 >> [1]: https://bugs.dpdk.org/show_bug.cgi?id=1716 >> >> Signed-off-by: Baoyuan Li >> Signed-off-by: Hengqi Chen >> --- >> drivers/net/virtio/virtio_rxtx.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c >> index edecd2011f..ab97f03d7d 100644 >> --- a/drivers/net/virtio/virtio_rxtx.c >> +++ b/drivers/net/virtio/virtio_rxtx.c >> @@ -1873,7 +1873,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf >> **tx_pkts, uint16_t nb_pkts) >> >> nb_used = virtqueue_nused(vq); >> >> - if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh)) >> + if (likely(vq->vq_free_cnt < vq->vq_free_thresh)) >> virtio_xmit_cleanup(vq, nb_used); >> >> for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) { >> -- >> 2.43.5 >