From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Olivier Matz <olivier.matz@6wind.com>, dev@dpdk.org
Cc: stephen@networkplumber.org, mst@redhat.com, yuanhan.liu@linux.intel.com
Subject: Re: [dpdk-dev] [PATCH 1/2] mbuf: add rte_pktmbuff_reset_headroom function
Date: Tue, 4 Oct 2016 13:51:39 +0200 [thread overview]
Message-ID: <41ca04b5-26d6-20eb-baf2-6a34fc003d2b@redhat.com> (raw)
In-Reply-To: <8b1847c7-e1a7-7477-8937-1e49c3ec0a8f@6wind.com>
On 10/03/2016 06:11 PM, Olivier Matz wrote:
> Hi Maxime,
>
> On 09/29/2016 02:20 PM, Maxime Coquelin wrote:
>> Some application use rte_mbuf_raw_alloc() function to improve
>> performance by not resetting mbuf's fields to their default state.
>>
>> This can be however problematic for mbuf consumers that need some
>> headroom, meaning that data_off field gets decremented after
>> allocation. When the mbuf is re-used afterwards, there might not
>> be enough room for the consumer to prepend anything, if the data_off
>> field is not reset to its default value.
>>
>> This patch adds a new rte_pktmbuf_reset_headroom() function that
>> applications can call to reset the data_off field.
>> This patch also replaces current data_off affectations in the mbuf
>> lib with a call to this function.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>
> Sounds like a good idea. Just one small comment below.
>
>>
>> /**
>> + * Reset the data_off field of a packet mbuf to its default value.
>> + *
>> + * The given mbuf must have only one segment.
>> + *
>> + * @param m
>> + * The packet mbuf's data_off field has to be reset.
>> + */
>> +static inline void rte_pktmbuf_reset_headroom(struct rte_mbuf *m)
>> +{
>> + m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
>> +}
>
> Maybe we should also highlight in the API comment that the segment
> should be empty.
Good point. I'll change to:
The given mbuf must have only one segment, which should be empty.
Thanks,
Maxime
prev parent reply other threads:[~2016-10-04 11:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-29 12:20 Maxime Coquelin
2016-09-29 12:20 ` [dpdk-dev] [PATCH 2/2] app/testpmd/txonly: Reset headroom after raw packet allocation Maxime Coquelin
2016-10-03 16:11 ` [dpdk-dev] [PATCH 1/2] mbuf: add rte_pktmbuff_reset_headroom function Olivier Matz
2016-10-04 11:51 ` Maxime Coquelin [this message]
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