From: Matthew Wilcox <willy@infradead.org>
To: Steve French <smfrench@gmail.com>
Cc: Jeff Layton <jlayton@redhat.com>,
David Howells <dhowells@redhat.com>,
Trond Myklebust <trondmy@hammerspace.com>,
Anna Schumaker <anna.schumaker@netapp.com>,
Steve French <sfrench@samba.org>,
Dominique Martinet <asmadeus@codewreck.org>,
CIFS <linux-cifs@vger.kernel.org>,
ceph-devel@vger.kernel.org, linux-cachefs@redhat.com,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-mm <linux-mm@kvack.org>,
linux-afs@lists.infradead.org,
v9fs-developer@lists.sourceforge.net,
Christoph Hellwig <hch@lst.de>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-nfs <linux-nfs@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Wysochanski <dwysocha@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
William Kucharski <william.kucharski@oracle.com>,
Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [PATCH 00/33] Network fs helper library & fscache kiocb API [ver #3]
Date: Tue, 23 Feb 2021 20:27:42 +0000 [thread overview]
Message-ID: <20210223202742.GM2858050@casper.infradead.org> (raw)
In-Reply-To: <CAH2r5mv+AdiODH1TSL+SOQ5qpZ25n7Ysrp+iYxauX9sD8ehhVQ@mail.gmail.com>
On Mon, Feb 15, 2021 at 11:22:20PM -0600, Steve French wrote:
> On Mon, Feb 15, 2021 at 8:10 PM Matthew Wilcox <willy@infradead.org> wrote:
> > The switch from readpages to readahead does help in a couple of corner
> > cases. For example, if you have two processes reading the same file at
> > the same time, one will now block on the other (due to the page lock)
> > rather than submitting a mess of overlapping and partial reads.
>
> Do you have a simple repro example of this we could try (fio, dbench, iozone
> etc) to get some objective perf data?
I don't. The problem was noted by the f2fs people, so maybe they have a
reproducer.
> My biggest worry is making sure that the switch to netfs doesn't degrade
> performance (which might be a low bar now since current network file copy
> perf seems to signifcantly lag at least Windows), and in some easy to understand
> scenarios want to make sure it actually helps perf.
I had a question about that ... you've mentioned having 4x4MB reads
outstanding as being the way to get optimum performance. Is there a
significant performance difference between 4x4MB, 16x1MB and 64x256kB?
I'm concerned about having "too large" an I/O on the wire at a given time.
For example, with a 1Gbps link, you get 250MB/s. That's a minimum
latency of 16us for a 4kB page, but 16ms for a 4MB page.
"For very simple tasks, people can perceive latencies down to 2 ms or less"
(https://danluu.com/input-lag/)
so going all the way to 4MB I/Os takes us into the perceptible latency
range, whereas a 256kB I/O is only 1ms.
So could you do some experiments with fio doing direct I/O to see if
it takes significantly longer to do, say, 1TB of I/O in 4MB chunks vs
256kB chunks? Obviously use threads to keep lots of I/Os outstanding.
next prev parent reply other threads:[~2021-02-23 20:28 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-15 15:44 [PATCH 00/33] Network fs helper library & fscache kiocb API [ver #3] David Howells
2021-02-15 15:44 ` [PATCH 01/33] iov_iter: Add ITER_XARRAY David Howells
2021-02-15 15:44 ` [PATCH 02/33] mm: Add an unlock function for PG_private_2/PG_fscache David Howells
2021-02-16 10:26 ` Christoph Hellwig
2021-02-15 15:44 ` [PATCH 03/33] mm: Implement readahead_control pageset expansion David Howells
2021-02-16 10:32 ` Christoph Hellwig
2021-02-16 13:22 ` Matthew Wilcox
2021-02-17 14:36 ` Mike Marshall
2021-02-17 15:42 ` David Howells
2021-02-17 16:59 ` Mike Marshall
2021-02-17 22:20 ` David Howells
2021-02-16 11:48 ` David Howells
2021-02-17 16:13 ` Matthew Wilcox
2021-02-17 22:34 ` David Howells
2021-02-17 22:49 ` Matthew Wilcox
2021-02-18 17:47 ` David Howells
2021-02-15 15:45 ` [PATCH 04/33] vfs: Export rw_verify_area() for use by cachefiles David Howells
2021-02-16 10:26 ` Christoph Hellwig
2021-02-16 11:55 ` David Howells
2021-02-15 15:45 ` [PATCH 05/33] netfs: Make a netfs helper module David Howells
2021-02-15 15:45 ` [PATCH 06/33] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-02-15 15:45 ` [PATCH 07/33] netfs, mm: Add unlock_page_fscache() and wait_on_page_fscache() David Howells
2021-02-15 15:45 ` [PATCH 08/33] netfs: Provide readahead and readpage netfs helpers David Howells
2021-02-15 15:45 ` [PATCH 09/33] netfs: Add tracepoints David Howells
2021-02-15 15:46 ` [PATCH 10/33] netfs: Gather stats David Howells
2021-02-15 15:46 ` [PATCH 11/33] netfs: Add write_begin helper David Howells
2021-02-15 15:46 ` [PATCH 12/33] netfs: Define an interface to talk to a cache David Howells
2021-02-15 15:46 ` [PATCH 13/33] netfs: Hold a ref on a page when PG_private_2 is set David Howells
2021-02-15 18:05 ` [PATCH 00/33] Network fs helper library & fscache kiocb API [ver #3] Jeff Layton
2021-02-16 0:40 ` Steve French
2021-02-16 2:10 ` Matthew Wilcox
2021-02-16 5:18 ` Steve French
2021-02-16 5:22 ` Steve French
2021-02-23 20:27 ` Matthew Wilcox [this message]
2021-02-24 4:57 ` Steve French
2021-02-24 13:32 ` David Howells
2021-02-24 15:51 ` Matthew Wilcox
2021-02-16 11:01 ` Jeff Layton
2021-02-15 22:46 ` [PATCH 34/33] netfs: Use in_interrupt() not in_softirq() David Howells
2021-02-16 8:42 ` Christoph Hellwig
2021-02-16 9:06 ` Sebastian Andrzej Siewior
2021-02-16 9:29 ` David Howells
2021-02-16 9:30 ` Christoph Hellwig
2021-02-18 14:02 ` [PATCH 34/33] netfs: Pass flag rather than use in_softirq() David Howells
2021-02-18 15:06 ` Marc Dionne
2021-02-18 15:16 ` Marc Dionne
2021-02-19 9:01 ` Sebastian Andrzej Siewior
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