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From: Jiufei Xue <jiufei.xue@linux.alibaba.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: overlayfs <linux-unionfs@vger.kernel.org>,
	Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: [Regression] performance regression since v4.19
Date: Tue, 12 Nov 2019 15:53:43 +0800	[thread overview]
Message-ID: <1086cadc-53c3-effd-5ba3-797a015944b5@linux.alibaba.com> (raw)

Hi Miklos,

A performance regression is observed since linux v4.19 when we do aio
test using fio with iodepth 128 on overlayfs. And we found that queue
depth of the device is always 1 which is unexpected. 

After investigation, it is found that commit 16914e6fc7
(“ovl: add ovl_read_iter()”) and commit 2a92e07edc
(“ovl: add ovl_write_iter()”) use do_iter_readv_writev() to submit
requests to real filesystem. Async IOs are converted to sync IOs here
and cause performance regression.

I wondered that is this a design flaw or supposed to be.

Thanks a lot,
Jiufei

             reply	other threads:[~2019-11-12  7:53 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-12  7:53 Jiufei Xue [this message]
2019-11-12  9:12 ` [Regression] performance regression since v4.19 Miklos Szeredi
2019-11-12 10:48   ` Amir Goldstein
2019-11-12 11:24     ` Miklos Szeredi
2019-11-13  6:33     ` Jiufei Xue
2019-11-13  6:31   ` Jiufei Xue

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