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Message-ID: <0293d72e-8d57-42c2-bb11-a7a553675ae6@huawei.com>
Date: Fri, 30 Aug 2024 11:48:45 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Youling Tang <youling.tang@...ux.dev>
CC: <linux-bcachefs@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Youling
Tang <tangyouling@...inos.cn>, Kent Overstreet <kent.overstreet@...ux.dev>
Subject: Re: [PATCH] bcachefs: Remove the handling of bch2_trans_iter_exit()
in __bch2_bkey_get_iter()
On 2024/8/30 9:19, Youling Tang wrote:
> On 2024/8/23 22:51, Kent Overstreet wrote:
>
>> On Fri, Aug 23, 2024 at 02:07:20PM GMT, Youling Tang wrote:
>>> On 23/08/2024 11:55, Kent Overstreet wrote:
>>>> On Fri, Aug 23, 2024 at 11:19:55AM GMT, Youling Tang wrote:
>>>>> From: Youling Tang <tangyouling@...inos.cn>
>>>>>
>>>>> - Reduces bkey_err() calls.
>>>>> - Avoid redundant calls to bch2_trans_iter_exit() in some functions.
>>>> no, a function that returns an error should clean up after itself
>>> Yes, functions should self-clean when they fail.
>>>
>>> However, there are repeated calls to bch2_trans_iter_exit in
>>> some functions, take lookup_inode() as an example,
>>>
>>> When bkey_err(k) returns a non-zero, call bch2_trans_iter_exit()
>>> once in bch2_bkey_get_iter(). It is then called again in
>>> lookup_inode() via 'goto err'. (We can correct it by simply changing
>>> it to 'return ret', but there are many similar cases.)
>> I'm aware, but I'm not looking to microoptimize at the expense of making
>> the code more fragile and less clear, especially right now when the
>> priority is stabilizing and fixing bugs.
>>
>> If you were also doing performance testing and could show that it
>> makes a measurable difference I'd consider it. Did you even look at the
>> assembly output for any of these functions? CSE might be optimizing away
>> the redundant calls.
> I haven't performed the corresponding performance testing. Looking at
> the assembly code, taking `lookup_inode()` as an example,
>
I think his point is that your modification is error-free, but improving
readability is not a high priority at the moment unless it actually
affects performance. There might currently be a shortage of manpower,
with many features to be completed and bugs to be fixed.
> Before the patch,
> 142f: 74 96 je 13c7 <lookup_inode+0x117>
> 1431: 48 8d b5 68 ff ff ff lea -0x98(%rbp),%rsi
> 1438: 4c 89 e7 mov %r12,%rdi
> 143b: e8 00 00 00 00 call 1440 <lookup_inode+0x190>
> 1440: eb b4 jmp 13f6 <lookup_inode+0x146>
> 1442: e8 00 00 00 00 call 1447 <lookup_inode+0x197>
> 1447: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
> 144e: 00 00
>
> After,
> 111f: 74 96 je 10b7 <lookup_inode+0x117>
> 1121: eb c3 jmp 10e6 <lookup_inode+0x146>
> 1123: e8 00 00 00 00 call 1128 <lookup_inode+0x188>
> 1128: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
> 112f: 00
>
> The following three assembly instructions have been reduced,
> 1431: 48 8d b5 68 ff ff ff lea -0x98(%rbp),%rsi
> 1438: 4c 89 e7 mov %r12,%rdi
> 143b: e8 00 00 00 00 call 1440 <lookup_inode+0x190>
>
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