From: Aleksandr Lyapunov <alyapunov@tarantool.org>
To: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>,
tarantool-patches@dev.tarantool.org, tsafin@tarantool.org,
gorcunov@gmail.com
Subject: Re: [Tarantool-patches] [PATCH 2/2] uuid: fix unaligned memory access
Date: Tue, 19 May 2020 10:28:33 +0300 [thread overview]
Message-ID: <f0774d12-0fdd-c922-05e3-e299640d6187@tarantool.org> (raw)
In-Reply-To: <e7a1a29d-c30b-9800-b55f-0f9ce00f8c4e@tarantool.org>
On 5/19/20 12:17 AM, Vladislav Shpilevoy wrote:
>
> Yeah, well. This is the same like saying that we degrade performance
> when we do OOM checks. Unaligned memory access is UB. This is a bug.
It's not the same. You could see I propose a solution that both violates no
rules and have the best performance. It's very far from just a complain.
>> I would suggest to use memcmp in this case.
>> It's portable and allows a compiler to generate the best possible code.
>> I've measured it (gcc) and memcmp version is twice faster than your solution.
>> Even for _is_nil method it's better to use memcmp with statically allocated zero buffer.
> Could you please show the benchmark? I did my own, and I can't see any
> significant difference. The present difference is so small, that it
> looks like jitter. Both in is_nil and is_eq.
>
> I did a very simple bench in Lua, without any GCed objects.
I fear that Lua is not suitable for performance tests.
Here you are: https://pastebin.com/VXkS1v6M
Also please take a look at disasm: https://godbolt.org/z/s6Cti4
next prev parent reply other threads:[~2020-05-19 7:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 23:03 [Tarantool-patches] [PATCH 0/2] Sanitize uuid and bit alignment Vladislav Shpilevoy
2020-05-15 23:03 ` [Tarantool-patches] [PATCH 1/2] bit: fix unaligned memory access and UB bit shift Vladislav Shpilevoy
2020-05-21 14:37 ` Timur Safin
2020-05-15 23:03 ` [Tarantool-patches] [PATCH 2/2] uuid: fix unaligned memory access Vladislav Shpilevoy
2020-05-18 12:55 ` Aleksandr Lyapunov
2020-05-18 21:17 ` Vladislav Shpilevoy
2020-05-19 7:28 ` Aleksandr Lyapunov [this message]
2020-05-19 8:34 ` Timur Safin
2020-05-19 21:24 ` Vladislav Shpilevoy
2020-05-20 8:18 ` Aleksandr Lyapunov
2020-05-20 21:38 ` Vladislav Shpilevoy
2020-05-21 8:28 ` Aleksandr Lyapunov
2020-05-21 14:37 ` Timur Safin
2020-05-21 19:33 ` [Tarantool-patches] [PATCH 0/2] Sanitize uuid and bit alignment Vladislav Shpilevoy
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