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To: Stephen Hemminger <stephen@networkplumber.org>
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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
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Date: Tue, 2 Oct 2018 10:03:35 +0100
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Subject: Re: [dpdk-dev] [PATCH v8 01/21] mem: add length to memseg list
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On 01-Oct-18 6:01 PM, Stephen Hemminger wrote:
> On Mon, 1 Oct 2018 13:56:09 +0100
> Anatoly Burakov <anatoly.burakov@intel.com> wrote:
>
>> diff --git a/lib/librte_eal/common/include/rte_eal_memconfig.h b/lib/librte_eal/common/include/rte_eal_memconfig.h
>> index aff0688dd..1d8b0a6fe 100644
>> --- a/lib/librte_eal/common/include/rte_eal_memconfig.h
>> +++ b/lib/librte_eal/common/include/rte_eal_memconfig.h
>> @@ -30,6 +30,7 @@ struct rte_memseg_list {
>> uint64_t addr_64;
>> /**< Makes sure addr is always 64-bits */
>> };
>> + size_t len; /**< Length of memory area covered by this memseg list. */
>> int socket_id; /**< Socket ID for all memsegs in this list. */
>> uint64_t page_sz; /**< Page size for all memsegs in this list. */
>> volatile uint32_t version; /**< version number for multiprocess sync. */
>
> If you are going to break ABI, why not try and rearrange to eliminate holes:
>
> Output of pahole (on x86 64 bit):
>
> struct rte_memseg_list {
> union {
> void * base_va; /* 0 8 */
> uint64_t addr_64; /* 0 8 */
> }; /* 0 8 */
> size_t len; /* 8 8 */
> int socket_id; /* 16 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> uint64_t page_sz; /* 24 8 */
> volatile uint32_t version; /* 32 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> struct rte_fbarray memseg_arr; /* 40 96 */
>
> /* XXX last struct has 4 bytes of padding */
>
> /* size: 136, cachelines: 3, members: 6 */
> /* sum members: 128, holes: 2, sum holes: 8 */
> /* paddings: 1, sum paddings: 4 */
> /* last cacheline: 8 bytes */
> };
>
Hi Stephen,
This data structure isn't performance-critical in any remote sense, but
sure, I can do that.
--
Thanks,
Anatoly