[dpdk-dev] [PATCH] ring: relax alignment constraint on ring structure
Burakov, Anatoly
anatoly.burakov at intel.com
Fri May 25 16:57:07 CEST 2018
On 25-May-18 1:18 PM, Burakov, Anatoly wrote:
> On 25-May-18 11:59 AM, Burakov, Anatoly wrote:
>> On 03-Apr-18 2:26 PM, Olivier Matz wrote:
>>> The initial objective of
>>> commit d9f0d3a1ffd4 ("ring: remove split cacheline build setting")
>>> was to add an empty cache line betwee, the producer and consumer
>>> data (on platform with cache line size = 64B), preventing from
>>> having them on adjacent cache lines.
>>>
>>> Following discussion on the mailing list, it appears that this
>>> also imposes an alignment constraint that is not required.
>>>
>>> This patch removes the extra alignment constraint and adds the
>>> empty cache lines using padding fields in the structure. The
>>> size of rte_ring structure and the offset of the fields remain
>>> the same on platforms with cache line size = 64B:
>>>
>>> rte_ring = 384
>>> rte_ring.name = 0
>>> rte_ring.flags = 32
>>> rte_ring.memzone = 40
>>> rte_ring.size = 48
>>> rte_ring.mask = 52
>>> rte_ring.prod = 128
>>> rte_ring.cons = 256
>>>
>>> But it has an impact on platform where cache line size is 128B:
>>>
>>> rte_ring = 384 -> 768
>>> rte_ring.name = 0
>>> rte_ring.flags = 32
>>> rte_ring.memzone = 40
>>> rte_ring.size = 48
>>> rte_ring.mask = 52
>>> rte_ring.prod = 128 -> 256
>>> rte_ring.cons = 256 -> 512
>>>
>>> Link: http://dpdk.org/dev/patchwork/patch/25039/
>>> Suggested-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
>>> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
>>> ---
>>
>> This patch causes eal_flags_autotest to hang on FreeBSD. Root cause at
>> this time is unknown, but this is a weird one - the test seems to hang
>> while doing read() in bsd/eal_thread.c:59. Reverting this patch on top
>> of rc5 results in eal_flags_autotest passing.
>>
>
> Further investigation shows that for some reason, if Enter is pressed
> while the test is seemingly "hung", it continues and passes. Or rather,
> it hangs on one test, and if Enter is pressed, it finishes that test and
> hangs on another, after which pressing Enter again will result in test
> succeeding. Weird...
>
This patch is OK, the problem is in the test :) With this patch, it
apparently blew up in just the right way, but really, the EAL flags
autotest is wrong on FreeBSD because it launches primary processes with
'--no-shconf' option, which corrupt main process's memory. For some
reason this only began manifesting with this patch.
--
Thanks,
Anatoly
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