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[129.215.91.156]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7fb919bsm35949025f8f.34.2025.11.25.11.49.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Nov 2025 11:49:42 -0800 (PST) Date: Tue, 25 Nov 2025 19:49:42 +0000 From: Karim Manaouil To: Carlos Maiolino Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Karim Manaouil Subject: Too many xfs-conv kworker threads Message-ID: <20251125194942.iphwjfx2a4bw6i7g@wrangler> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi folks, I have four NVMe SSDs on RAID0 with XFS and upstream Linux kernel 6.15 with commit id e5f0a698b34ed76002dc5cff3804a61c80233a7a. The setup can achieve 25GB/s and more than 2M IOPS. The CPU is a dual socket 24-cores AMD EPYC 9224. I am running thpchallenge-fio from mmtests (its purpose is described here [1]). It's a fio job that inefficiently writes a large number of 64K files. On a system with 128GiB of RAM, it could create up to 100K files. A typical fio config looks like this: [global] direct=0 ioengine=sync blocksize=4096 invalidate=0 fallocate=none create_on_open=1 [writer] nrfiles=785988 filesize=65536 readwrite=write numjobs=4 filename_format=$jobnum/workfile.$filenum I noticed that, at some point, top reports around 42650 sleeping tasks, example: Tasks: 42651 total, 1 running, 42650 sleeping, 0 stopped, 0 zombie This is a test machine from a fresh boot running vanilla Debian. After checking, it turned out, it was a massive list of xfs-conv kworkers. Something like this (truncated): 58214 ? I 0:00 [kworker/47:203-xfs-conv/md127] 58215 ? I 0:00 [kworker/47:204-xfs-conv/md127] 58216 ? I 0:00 [kworker/47:205-xfs-conv/md127] 58217 ? I 0:00 [kworker/47:206-xfs-conv/md127] 58219 ? I 0:00 [kworker/12:539-xfs-conv/md127] 58220 ? I 0:00 [kworker/12:540-xfs-conv/md127] 58221 ? I 0:00 [kworker/12:541-xfs-conv/md127] 58222 ? I 0:00 [kworker/12:542-xfs-conv/md127] 58223 ? I 0:00 [kworker/12:543-xfs-conv/md127] 58224 ? I 0:00 [kworker/12:544-xfs-conv/md127] 58225 ? I 0:00 [kworker/12:545-xfs-conv/md127] 58227 ? I 0:00 [kworker/38:155-xfs-conv/md127] 58228 ? I 0:00 [kworker/38:156-xfs-conv/md127] 58230 ? I 0:00 [kworker/38:158-xfs-conv/md127] 58233 ? I 0:00 [kworker/38:161-xfs-conv/md127] 58235 ? I 0:00 [kworker/8:537-xfs-conv/md127] 58237 ? I 0:00 [kworker/8:539-xfs-conv/md127] 58238 ? I 0:00 [kworker/8:540-xfs-conv/md127] 58239 ? I 0:00 [kworker/8:541-xfs-conv/md127] 58240 ? I 0:00 [kworker/8:542-xfs-conv/md127] 58241 ? I 0:00 [kworker/8:543-xfs-conv/md127] It seems like the kernel is creating too many kworkers on each CPU. I am not sure if this has any effect on performance, but potentially, there is some scheduling overhead?! Is this a healthy amount of kworkers? Is this even needed? Even if we are trying to write to ~80k small files by four parallel threads? [1] https://lwn.net/Articles/770235/ -- ~karim