linux-kernel - Recent slowdown in single object builds

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Message-ID: <d60946a1-fde3-ee6f-683a-42a611768bbf@kernel.dk>
Date:   Fri, 15 Nov 2019 16:10:42 -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: Recent slowdown in single object builds

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...

-- 
Jens Axboe