Hi Pablo,

Please see inline.

Thanks,
Anoob
On 10-07-2018 17:18, De Lara Guarch, Pablo wrote:

External Email

quoted

-----Original Message-----
From: De Lara Guarch, Pablo
Sent: Tuesday, July 10, 2018 12:17 PM
To: 'Anoob Joseph' <redacted>; Doherty, Declan
[off-list ref]
Cc: 'Akhil Goyal' <redacted>; 'Ankur Dwivedi'
[off-list ref]; 'Jerin Jacob'
[off-list ref]; 'Narayana Prasad'
[off-list ref]; 'dev@dpdk.org'
[off-list ref]
Subject: RE: [PATCH v1 2/3] app/crypto-perf: honour cryptodev's min
headroom/tailroom

quoted

-----Original Message-----
From: De Lara Guarch, Pablo
Sent: Tuesday, July 10, 2018 12:08 PM
To: 'Anoob Joseph' <redacted>; Doherty, Declan
[off-list ref]
Cc: Akhil Goyal <redacted>; Ankur Dwivedi
[off-list ref]; Jerin Jacob
[off-list ref]; Narayana Prasad
[off-list ref]; dev@dpdk.org
Subject: RE: [PATCH v1 2/3] app/crypto-perf: honour cryptodev's min
headroom/tailroom

quoted

-----Original Message-----
From: Anoob Joseph [mailto:anoob.joseph@caviumnetworks.com]
Sent: Wednesday, July 4, 2018 2:56 PM
To: Doherty, Declan <redacted>; De Lara Guarch,
Pablo [off-list ref]
Cc: Anoob Joseph <redacted>; Akhil Goyal
[off-list ref]; Ankur Dwivedi
[off-list ref]; Jerin Jacob
[off-list ref]; Narayana Prasad
[off-list ref]; dev@dpdk.org
Subject: [PATCH v1 2/3] app/crypto-perf: honour cryptodev's min
headroom/tailroom

Crypto dev would specify its headroom and tailroom requirement and
the application is expected to honour this while creating buffers.

Signed-off-by: Anoob Joseph <redacted>

...

quoted

--- a/app/test-crypto-perf/cperf_test_common.c
+++ b/app/test-crypto-perf/cperf_test_common.c

...

quoted

fill_multi_seg_mbuf(struct rte_mbuf *m, struct rte_mempool *mp,
           m->buf_iova = next_seg_phys_addr;
           next_seg_phys_addr += mbuf_hdr_size + segment_sz;
           m->buf_len = segment_sz;
-         m->data_len = segment_sz;
+         m->data_len = data_len;

-         /* No headroom needed for the buffer */
-         m->data_off = 0;
+         /* Use headroom specified for the buffer */
+         m->data_off = headroom;

Headroom is only applicable for the first segment/s.
This is adding headroom in all the segments, which looks wrong.

I think "max_size" needs to be recalculated in "cperf_alloc_common_memory",
adding headroom and tailroom size, which will potentially increase the number
of segments required.
Then, headroom size needs to be checked in case it is bigger than segment size,
so data might need to start in the next segment.
Similar thing for tailroom.

Actually, forget about this. I have been thinking about it, and it looks artificial to do this.
Generally, in a mbuf pool, headroom is the same for all mbufs/segments.

Do I need to revisit this patch? Or is this fine?

In any case, I have a concern though about this. Headroom size is got from a compile time option:
CONFIG_RTE_PKTMBUF_HEADROOM=128. PMDs generally use this value to set "data_off",
but they could use another different value.
So what happens if min_mbuf_headroom is more than this value?
since this is not configurable, this won't work.

Since this is a PMD specific issue, we can have an extra check in the 
driver to make sure "CONFIG_RTE_PKTMBUF_HEADROOM">= min_mbuf_headroom 
for the PMD. If this check isn't satisfied, the driver probe would fail. 
Is this approach fine?

If application chooses to ignore CONFIG_RTE_PKTMBUF_HEADROOM altogether, 
then it will be a problem for most PMDs. With protocol offloads etc, 
headroom would be used internally, right?

Also, generally, headroom and tailroom are used for encapsulation, so I am not sure if this is the best place.

Is your concern about whether there is enough space in headroom for 
encapsulation & PMD's usage? Application can probe the individual values 
and see if there is enough space, right? In our use case, the headroom 
requirement is 24 bytes & tailroom requirement is 8 bytes.

What about using the private size of the mbuf? That is actually configurable, even though that data is not necessarily contiguous
to the mbuf data.

That memory being non contiguous is the problem. We use the headroom to 
specify the command so that one single buffer can be sent to the h/w for 
processing. If there is a gap of 128 bytes (headroom which lies in 
between private space & data), it will not work.

Sorry for the confusion and this last minute concern.

Thanks,
Pablo

quoted

Thanks,
Pablo