From: Al Viro <viro@zeniv.linux.org.uk>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Dave Jiang <dave.jiang@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
Matthew Wilcox <willy@infradead.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>,
"Kani, Toshi" <toshi.kani@hpe.com>,
"Norton, Scott J" <scott.norton@hpe.com>,
"Tadakamadla, Rajesh" <rajesh.tadakamadla@hpe.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-nvdimm@lists.01.org
Subject: Re: [RFC v2] nvfs: a filesystem for persistent memory
Date: Sun, 10 Jan 2021 23:40:42 +0000 [thread overview]
Message-ID: <20210110234042.GX3579531@ZenIV.linux.org.uk> (raw)
In-Reply-To: <alpine.LRH.2.02.2101101410230.7245@file01.intranet.prod.int.rdu2.redhat.com>
On Sun, Jan 10, 2021 at 04:14:55PM -0500, Mikulas Patocka wrote:
> That's a good point. I split nvfs_rw_iter to separate functions
> nvfs_read_iter and nvfs_write_iter - and inlined nvfs_rw_iter_locked into
> both of them. It improved performance by 1.3%.
>
> > Not that it had been more useful on the write side, really,
> > but that's another story (nvfs_write_pages() handling of
> > copyin is... interesting). Let's figure out what's going
> > on with the read overhead first...
> >
> > lib/iov_iter.c primitives certainly could use massage for
> > better code generation, but let's find out how much of the
> > PITA is due to those and how much comes from you fighing
> > the damn thing instead of using it sanely...
>
> The results are:
>
> read: 6.744s
> read_iter: 7.417s
> read_iter - separate read and write path: 7.321s
> Al's read_iter: 7.182s
> Al's read_iter with _copy_to_iter: 7.181s
So
* overhead of hardening stuff is noise here
* switching to more straightforward ->read_iter() cuts
the overhead by about 1/3.
Interesting... I wonder how much of that is spent in
iterate_and_advance() glue inside copy_to_iter() here. There's
certainly quite a bit of optimizations possible in those
primitives and your usecase makes a decent test for that...
Could you profile that and see where is it spending
the time, on instruction level?
next prev parent reply other threads:[~2021-01-10 23:42 UTC|newest]
Thread overview: 30+ 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
2021-01-12 13:45 ` Zhongwei Cai
2021-01-12 14:06 ` David Laight
2021-01-13 16:44 ` Mikulas Patocka
2021-01-15 9:40 ` Zhongwei Cai
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
2021-01-21 16:30 ` Zhongwei Cai
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
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 [this message]
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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