From: Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>
To: Boris Brezillon
<boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
Cc: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>,
linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>,
Przemyslaw Sroka <psroka-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Arkadiusz Golec <agolec-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Alan Douglas <adouglas-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Bartosz Folta <bfolta-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Damian Kos <dkos-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Alicja Jurasik-Urbaniak
<alicja-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Jan Kotas <jank-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Cyprian Wronka <cwronka-vna1KIf7WgpBDgjK7y7TUQ@public.gmane.org>,
Alexandre Belloni
<alexandre.belloni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>,
Thomas Petazzoni
<thomas.petazzoni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>,
Nishanth Menon <nm-l0cyMroinI0@public.gmane.org>,
Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
Ian Campbell
<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
Kumar Gala <galak@co>
Subject: Re: [RFC 2/5] i3c: Add core I3C infrastructure
Date: Wed, 13 Dec 2017 17:51:55 +0100 [thread overview]
Message-ID: <20171213165155.GA6003@kroah.com> (raw)
In-Reply-To: <20171213172043.24e4d4bc@bbrezillon>
On Wed, Dec 13, 2017 at 05:20:43PM +0100, Boris Brezillon wrote:
> Hi Greg,
>
> On Tue, 1 Aug 2017 19:13:27 -0700
> Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
>
> > > > > Unless you see a good reason to not use a R/W lock, I'd like to keep it
> > > > > this way because master IPs are likely to implement advanced queuing
> > > > > mechanism (allows one to queue new transfers even if the master is
> > > > > already busy processing other requests), and serializing things at the
> > > > > framework level will just prevent us from using this kind of
> > > > > optimization.
> > > >
> > > > Unless you can prove otherwise, using a rw lock is almost always worse
> > > > than just a mutex.
> > >
> > > Is it still true when it's taken in non-exclusive mode most of the
> > > time, and the time you spend in the critical section is non-negligible?
> > >
> > > I won't pretend I know better than you do what is preferable, it's just
> > > that the RW lock seemed appropriate to me for the situation I tried to
> > > described here.
> >
> > Again, measure it. If you can't measure it, then don't use it. Use a
> > simple lock instead. Seriously, don't make it more complex until you
> > really have to. It sounds like you didn't measure it at all, which
> > isn't good, please do so.
> >
>
> I'm resurrecting this thread because I finally had the time to implement
> message queuing in Cadence I3C master driver. So I did a test with 2
> I3C devices on the bus, and their drivers sending as much SDR messages
> as they can in 10s. Here are the results:
>
> | mutex | rwsem |
> ---------------------------------------
> dev1 | 19087 | 29532 |
> dev2 | 19341 | 29118 |
> =======================================
> total | 38428 | 58650 |
> msg/sec | ~3843 | ~5865 |
>
>
> The results I'm obtaining here are not so surprising since all normal
> transfers are taking the lock in read mode, so there's no contention.
> I didn't measure the impact on performances when there's one
> maintenance operation taking the lock in write mode and several normal
> transfers waiting for this lock, but really, maintenance operations are
> infrequent, and that's not where performance matters in our use case.
>
> I also did the same test with only one device doing transfers on the
> bus, and this time the mutex wins, but there's not a huge difference.
>
> | mutex | rwsem |
> ---------------------------------------
> total | 67116 | 66561 |
> msg/sec | ~6712 | ~6656 |
>
> Let me know if you want more information on the test procedure.
Nice, thanks for testing, so it is a real win here, good!
greg k-h
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next prev parent reply other threads:[~2017-12-13 16:51 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-31 16:24 [RFC 0/5] Add I3C subsystem Boris Brezillon
2017-07-31 16:24 ` [RFC 1/5] i2c: Export of_i2c_get_board_info() Boris Brezillon
2017-07-31 16:24 ` [RFC 2/5] i3c: Add core I3C infrastructure Boris Brezillon
2017-07-31 19:17 ` Wolfram Sang
2017-07-31 20:46 ` Boris Brezillon
2017-07-31 20:16 ` Arnd Bergmann
[not found] ` <CAK8P3a06GoMdKdn=3Cq0FUwYnjGX0oG+FQLjxfiasVDpbonWRw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-07-31 21:15 ` Boris Brezillon
2017-07-31 21:32 ` Peter Rosin
2017-07-31 21:42 ` Wolfram Sang
2017-08-01 16:47 ` Andrew F. Davis
2017-08-01 17:27 ` Wolfram Sang
2017-08-01 21:47 ` Boris Brezillon
2017-08-02 10:21 ` Wolfram Sang
2017-08-01 12:00 ` Arnd Bergmann
2017-08-01 12:29 ` Boris Brezillon
2017-08-01 13:11 ` Arnd Bergmann
2017-08-01 13:34 ` Boris Brezillon
2017-08-01 13:58 ` Boris Brezillon
2017-08-01 14:22 ` Arnd Bergmann
2017-08-01 15:14 ` Boris Brezillon
2017-08-01 20:16 ` Arnd Bergmann
2017-08-01 14:12 ` Wolfram Sang
2017-08-01 14:48 ` Boris Brezillon
2017-08-01 15:01 ` Wolfram Sang
2017-08-01 15:20 ` Boris Brezillon
2017-08-03 8:03 ` Boris Brezillon
2017-08-16 21:03 ` Geert Uytterhoeven
2017-08-17 7:48 ` Boris Brezillon
2017-08-01 1:40 ` Greg Kroah-Hartman
[not found] ` <20170801014021.GA20004-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2017-08-01 10:48 ` Boris Brezillon
2017-08-01 17:51 ` Greg Kroah-Hartman
2017-08-01 21:30 ` Boris Brezillon
2017-08-02 0:54 ` Greg Kroah-Hartman
2017-08-02 2:13 ` Greg Kroah-Hartman
[not found] ` <20170802021327.GB23033-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2017-12-13 16:20 ` Boris Brezillon
2017-12-13 16:51 ` Greg Kroah-Hartman [this message]
2017-08-17 9:03 ` Linus Walleij
2017-08-17 9:28 ` Boris Brezillon
[not found] ` <1501518290-5723-1-git-send-email-boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
2017-07-31 16:24 ` [RFC 3/5] dt-bindings: i3c: Document core bindings Boris Brezillon
2017-08-09 23:43 ` Rob Herring
2017-08-10 8:49 ` Boris Brezillon
2017-07-31 16:24 ` [RFC 4/5] i3c: master: Add driver for Cadence IP Boris Brezillon
2017-07-31 16:24 ` [RFC 5/5] dt-bindings: i3c: Document Cadence I3C master bindings Boris Brezillon
2017-07-31 19:17 ` [RFC 0/5] Add I3C subsystem Wolfram Sang
2017-07-31 20:40 ` Boris Brezillon
2017-07-31 20:47 ` Wolfram Sang
2017-12-12 19:58 ` Boris Brezillon
2017-12-12 22:01 ` Wolfram Sang
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