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To: Maxime Coquelin <maxime.coquelin@redhat.com>,
Ilya Maximets <i.maximets@ovn.org>, Flavio Leitner <fbl@sysclose.org>,
dev@dpdk.org
Cc: Shahaf Shuler <shahafs@mellanox.com>,
David Marchand <david.marchand@redhat.com>, Tiwei Bie <tiwei.bie@intel.com>,
Obrembski MichalX <michalx.obrembski@intel.com>,
Stokes Ian <ian.stokes@intel.com>
References: <20191015161727.32570-1-fbl@sysclose.org>
<20191015185951.6295-1-fbl@sysclose.org>
<ef8dc25d-c5fd-a146-48c1-259cad719e6f@redhat.com>
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<62fb6a50-d4ab-584d-8cb2-4820c141f137@redhat.com>
From: Ilya Maximets <i.maximets@ovn.org>
Message-ID: <2b963349-66d9-179d-b480-6e15263733f3@ovn.org>
Date: Wed, 16 Oct 2019 16:05:18 +0200
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Subject: Re: [dpdk-dev] [PATCH v5] vhost: add support for large buffers
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On 16.10.2019 15:46, Maxime Coquelin wrote:
>
>
> On 10/16/19 3:32 PM, Ilya Maximets wrote:
>> On 16.10.2019 13:13, Maxime Coquelin wrote:
>>>
>>>
>>> On 10/15/19 8:59 PM, Flavio Leitner wrote:
>>>> The rte_vhost_dequeue_burst supports two ways of dequeuing data.
>>>> If the data fits into a buffer, then all data is copied and a
>>>> single linear buffer is returned. Otherwise it allocates
>>>> additional mbufs and chains them together to return a multiple
>>>> segments mbuf.
>>>>
>>>> While that covers most use cases, it forces applications that
>>>> need to work with larger data sizes to support multiple segments
>>>> mbufs. The non-linear characteristic brings complexity and
>>>> performance implications to the application.
>>>>
>>>> To resolve the issue, add support to attach external buffer
>>>> to a pktmbuf and let the host provide during registration if
>>>> attaching an external buffer to pktmbuf is supported and if
>>>> only linear buffer are supported.
>>>>
>>>> Signed-off-by: Flavio Leitner <fbl@sysclose.org>
>>>> ---
>>>> doc/guides/prog_guide/vhost_lib.rst | 35 +++++++++
>>>> lib/librte_vhost/rte_vhost.h | 4 +
>>>> lib/librte_vhost/socket.c | 22 ++++++
>>>> lib/librte_vhost/vhost.c | 22 ++++++
>>>> lib/librte_vhost/vhost.h | 4 +
>>>> lib/librte_vhost/virtio_net.c | 109 ++++++++++++++++++++++++----
>>>> 6 files changed, 182 insertions(+), 14 deletions(-)
>>>>
>>>> - Changelog:
>>>> v5:
>>>> - fixed to destroy mutex if incompatible flags
>>>> v4:
>>>> - allow to use pktmbuf if there is exact space
>>>> - removed log message if the buffer is too big
>>>> - fixed the length to include align padding
>>>> - free allocated buf if shinfo fails
>>>> v3:
>>>> - prevent the new features to be used with zero copy
>>>> - fixed sizeof() usage
>>>> - fixed log msg indentation
>>>> - removed/replaced asserts
>>>> - used the correct virt2iova function
>>>> - fixed the patch's title
>>>> - OvS PoC code:
>>>> https://github.com/fleitner/ovs/tree/rte_malloc-v3
>>>> v2:
>>>> - Used rte_malloc() instead of another mempool as suggested by
>>>> Shahaf.
>>>> - Added the documentation section.
>>>> - Using driver registration to negotiate the features.
>>>> - OvS PoC code:
>>>>
>>>> https://github.com/fleitner/ovs/commit/8fc197c40b1d4fda331686a7b919e9e2b670dda7
>>>>
>>>
>>> Applied to dpdk-next-virtio/master.
>>
>> Thanks Maxime,
>>
>> But can we return back the mbuf allocation failure message?
>
> Good point, I missed it.
>
>> I mean:
>>
>> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
>> index 66f0c7206..f8af4e0b3 100644
>> --- a/lib/librte_vhost/virtio_net.c
>> +++ b/lib/librte_vhost/virtio_net.c
>> @@ -1354,8 +1354,11 @@ virtio_dev_pktmbuf_alloc(struct virtio_net *dev,
>> struct rte_mempool *mp,
>> {
>> struct rte_mbuf *pkt = rte_pktmbuf_alloc(mp);
>>
>> - if (unlikely(pkt == NULL))
>> + if (unlikely(pkt == NULL)) {
>> + RTE_LOG(ERR, VHOST_DATA,
>> + "Failed to allocate memory for mbuf.\n");
>> return NULL;
>> + }
>>
>> if (rte_pktmbuf_tailroom(pkt) >= data_len)
>> return pkt;
>> ---
>>
>> It's a hard failure that highlights some significant issues with
>> memory pool size or a mbuf leak.
>
> I agree, we need this error message.
>
>> We still have the message for subsequent chained mbufs, but not
>> for the first one. Without this error message we could never
>> notice that something is wrong with our memory pool. Only the
>> network traffic will stop flowing.
>> The message was very useful previously while catching the root
>> cause of the mbuf leak in OVS.
>>
>> I could send a separate patch for this if needed.
>
> We need a separate patch.
> If you want to do it, please do! Otherwise I'll do it.
OK. I'll send a patch soon.
Best regards, Ilya Maximets.