linux-kernel - Re: Recent slowdown in single object builds

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Date:   Sun, 17 Nov 2019 19:34:42 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Recent slowdown in single object builds

On 11/17/19 5:40 PM, Masahiro Yamada wrote:
> On Sun, Nov 17, 2019 at 1:57 AM Jens Axboe <axboe@...nel.dk> wrote:
>>
>> On 11/16/19 12:17 AM, Masahiro Yamada wrote:
>>> On Sat, Nov 16, 2019 at 8:10 AM Jens Axboe <axboe@...nel.dk> wrote:
>>>>
>>>> Hi,
>>>>
>>>> I've noticed that current -git is a lot slower at doing single object
>>>> builds than earlier kernels. Here's an example, building the exact same
>>>> file on 5.2 and -git:
>>>>
>>>> $ time make fs/io_uring.o
>>>> real    0m5.953s
>>>> user    0m5.402s
>>>> sys     0m0.649s
>>>>
>>>> vs 5.2 based (with all the backports, identical file):
>>>>
>>>> $ time make fs/io_uring.o
>>>> real    0m3.218s
>>>> user    0m2.968s
>>>> sys     0m0.520s
>>>>
>>>> Any idea what's going on here? It's almost twice as slow, which is
>>>> problematic...
> 
> 
> BTW, I am using a cheap machine based on Intel Core i7-6700K.
> I can build fs/io_uring.o (based on x86_64_defconfig) much faster.
> 
> 
> The slowdown (1.990 sec -> 2.861 sec) is not terrible for me.

For those of us that do single object builds all the time the slowdown
is pretty damn terrible. Granted that your 44% slowdown isn't as bad as
my 85% slowdown, but it's still a MASSIVE slowdown.

-- 
Jens Axboe