From: Matthew Wilcox <willy@infradead.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Steven Whitehouse <swhiteho@redhat.com>,
Eric Sandeen <esandeen@redhat.com>,
Dave Chinner <dchinner@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
Wang Jianchao <jianchao.wan9@gmail.com>,
"Tadakamadla, Rajesh" <rajesh.tadakamadla@hpe.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-nvdimm@lists.01.org
Subject: Re: Expense of read_iter
Date: Mon, 11 Jan 2021 00:18:05 +0000 [thread overview]
Message-ID: <20210111001805.GD35215@casper.infradead.org> (raw)
In-Reply-To: <alpine.LRH.2.02.2101101458420.7366@file01.intranet.prod.int.rdu2.redhat.com>
On Sun, Jan 10, 2021 at 04:19:15PM -0500, Mikulas Patocka wrote:
> I put counters into vfs_read and vfs_readv.
>
> After a fresh boot of the virtual machine, the counters show "13385 4".
> After a kernel compilation they show "4475220 8".
>
> So, the readv path is almost unused.
>
> My reasoning was that we should optimize for the "read" path and glue the
> "readv" path on the top of that. Currently, the kernel is doing the
> opposite - optimizing for "readv" and glueing "read" on the top of it.
But it's not about optimising for read vs readv. read_iter handles
a host of other cases, such as pread(), preadv(), AIO reads, splice,
and reads to in-kernel buffers.
Some device drivers abused read() vs readv() to actually return different
information, depending which you called. That's why there's now a
prohibition against both.
So let's figure out how to make iter_read() perform well for sys_read().
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next prev parent reply other threads:[~2021-01-11 0:18 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-07 13:15 [RFC v2] nvfs: a filesystem for persistent memory Mikulas Patocka
2021-01-07 15:11 ` Expense of read_iter Matthew Wilcox
2021-01-07 16:43 ` Mingkai Dong
[not found] ` <2041983017.5681521.1610459100858.JavaMail.zimbra@sjtu.edu.cn>
2021-01-12 14:06 ` David Laight
2021-01-13 16:44 ` Mikulas Patocka
[not found] ` <1224425872.715547.1610703643424.JavaMail.zimbra@sjtu.edu.cn>
2021-01-20 4:47 ` Dave Chinner
2021-01-20 14:18 ` Jan Kara
2021-01-20 15:12 ` Mikulas Patocka
2021-01-20 15:44 ` David Laight
2021-01-21 15:47 ` Matthew Wilcox
2021-01-21 16:06 ` Mikulas Patocka
2021-01-07 18:59 ` Mikulas Patocka
2021-01-10 6:13 ` Matthew Wilcox
2021-01-10 21:19 ` Mikulas Patocka
2021-01-11 0:18 ` Matthew Wilcox [this message]
2021-01-11 21:10 ` Mikulas Patocka
2021-01-11 10:11 ` David Laight
2021-01-10 16:20 ` [RFC v2] nvfs: a filesystem for persistent memory Al Viro
2021-01-10 16:51 ` Al Viro
2021-01-10 21:14 ` Mikulas Patocka
2021-01-10 23:40 ` Al Viro
2021-01-11 11:41 ` Mikulas Patocka
2021-01-11 10:29 ` David Laight
2021-01-11 11:44 ` Mikulas Patocka
2021-01-11 11:57 ` David Laight
2021-01-11 14:43 ` Al Viro
2021-01-11 14:54 ` David Laight
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