From: "Wang, Yipeng1" <yipeng1.wang@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>,
"De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>,
Steve Capper <Steve.Capper@arm.com>,
Ola Liljedahl <Ola.Liljedahl@arm.com>, nd <nd@arm.com>,
"Gobriel, Sameh" <sameh.gobriel@intel.com>
Subject: Re: [dpdk-dev] [PATCH 2/4] hash: add memory ordering to avoid race conditions
Date: Mon, 1 Oct 2018 22:41:56 +0000 [thread overview]
Message-ID: <D2C4A16CA39F7F4E8E384D204491D7A6614EA299@FMSMSX151.amr.corp.intel.com> (raw)
In-Reply-To: <AM6PR08MB3672DF53627F2EBE0000CF7398EE0@AM6PR08MB3672.eurprd08.prod.outlook.com>
>-----Original Message-----
>From: Honnappa Nagarahalli [mailto:Honnappa.Nagarahalli@arm.com]
>Sent: Sunday, September 30, 2018 3:21 PM
>To: Wang, Yipeng1 <yipeng1.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>; De Lara Guarch, Pablo
><pablo.de.lara.guarch@intel.com>
>Cc: dev@dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Steve Capper <Steve.Capper@arm.com>; Ola Liljedahl
><Ola.Liljedahl@arm.com>; nd <nd@arm.com>
>Subject: RE: [dpdk-dev] [PATCH 2/4] hash: add memory ordering to avoid race conditions
>
>>
>> Some general comments for the various __atomic_store/load added,
>>
>> 1. Although it passes the compiler check, but I just want to confirm that if we
>> should use GCC/clang builtins, or if There are higher level APIs in DPDK to do
>> atomic operations?
>>
>I have used gcc builtins (just like rte_ring does)
[Wang, Yipeng] I checked rte_ring, it also has a specific header for C11, since it is a C11
standard, do we need something similar here?
>
>> 2. We believe compiler will translate the atomic_store/load to regular MOV
>> instruction on Total Store Order architecture (e.g. X86_64). But we run the
>> perf test on x86 and here is the relative slowdown on lookup comparing to
>> master head. I am not sure if the performance drop comes from the atomic
>> buitins.
>>
>C11 atomics also block compiler reordering. Other than this, the retry loop is an addition to lookup.
>The patch also has the alignment corrected. I am not sure how is that affecting the perf numbers.
>
>> Keysize | single lookup | bulk lookup
>> 4 | 0.93 | 0.95
>> 8 | 0.95 | 0.96
>> 16 | 0.97 | 0.96
>> 32 | 0.97 | 1.00
>> 48 | 1.03 | 0.99
>> 64 | 1.04 | 0.98
>> 9 | 0.91 | 0.96
>> 13 | 0.97 | 0.98
>> 37 | 1.04 | 1.03
>> 40 | 1.02 | 0.98
>>
>I assume this is the data from the test cases in test_hash_perf.c file. I tried to reproduce this data, but my data is worse. Can you
>specify the actual test from test_hash_perf.c you are using (With locks/Pre-computed hash/With data/Elements in primary)?
>IMO, the differences you have provided are not high.
[Wang, Yipeng] I remember the performance data I used is the no-lock, without hash, with 8-byte data, in both primary and secondary.
I compared the master head to the one with your first two commits.
>
>> [Wang, Yipeng] I think even for current code, we need to check empty_slot.
>> Could you export this as a bug fix commit?
>>
>In the existing code, there is check 'if (!!key_idx & !rte_hash....)'. Are you referring to '!!key_idx'? I think this should be changed to
>'(key_idx != EMPTY_SLOT)'.
[Wang, Yipeng] Yeah, I guess I did not see that part. Then I guess it is no need to export as a bug fix for now since it is not a functional issue.
Your change is good.
next prev parent reply other threads:[~2018-10-01 22:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 17:12 [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 1/4] hash: correct key store element alignment Honnappa Nagarahalli
2018-09-27 23:58 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 2/4] hash: add memory ordering to avoid race conditions Honnappa Nagarahalli
2018-09-28 0:43 ` Wang, Yipeng1
2018-09-30 22:20 ` Honnappa Nagarahalli
2018-10-01 22:41 ` Wang, Yipeng1 [this message]
2018-10-01 10:42 ` Ola Liljedahl
2018-10-02 1:52 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys Honnappa Nagarahalli
2018-09-28 1:00 ` Wang, Yipeng1
2018-09-28 8:26 ` Bruce Richardson
2018-09-28 8:55 ` Van Haaren, Harry
2018-09-30 22:33 ` Honnappa Nagarahalli
2018-10-02 13:17 ` Van Haaren, Harry
2018-10-02 23:58 ` Wang, Yipeng1
2018-10-03 17:32 ` Honnappa Nagarahalli
2018-10-03 17:56 ` Wang, Yipeng1
2018-10-03 23:05 ` Ola Liljedahl
2018-10-04 3:32 ` Honnappa Nagarahalli
2018-10-04 3:54 ` Honnappa Nagarahalli
2018-10-04 19:16 ` Wang, Yipeng1
2018-09-30 23:05 ` Honnappa Nagarahalli
2018-10-01 22:56 ` Wang, Yipeng1
2018-10-03 0:16 ` Wang, Yipeng1
2018-10-03 17:39 ` Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 4/4] hash: enable lock-free reader-writer concurrency Honnappa Nagarahalli
2018-09-28 1:33 ` Wang, Yipeng1
2018-10-01 4:11 ` Honnappa Nagarahalli
2018-10-01 23:54 ` Wang, Yipeng1
2018-10-11 5:24 ` Honnappa Nagarahalli
2018-09-14 21:18 ` [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-26 14:36 ` Honnappa Nagarahalli
2018-09-27 23:45 ` Wang, Yipeng1
2018-09-28 21:11 ` Honnappa Nagarahalli
2018-10-02 0:30 ` Wang, Yipeng1
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