From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [RFC 0/2] drivers: spi/i2c: account completions as iowait Date: Mon, 3 Nov 2014 20:45:06 +0100 Message-ID: <20141103194506.GB1449@katana> References: <1414936689-2707-1-git-send-email-wsa@the-dreams.de> <20141103130222.1c53fa39@alan.etchedpixels.co.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="hQiwHBbRI9kgIhsi" Return-path: Content-Disposition: inline In-Reply-To: <20141103130222.1c53fa39-mUKnrFFms3BCCTY1wZZT65JpZx93mCW/@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: One Thousand Gnomes Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mark Brown , Peter Zijlstra , Ingo Molnar , Balbir Singh List-Id: linux-i2c@vger.kernel.org --hQiwHBbRI9kgIhsi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > > However, researching the net, users currently interpret iowait entirely= as > > blkio wait. Furthermore, io_schedule() calls delayacct_blkio_{start|end= }() which > > worked fine for my tests with I2C but might show that iowait was really= meant as > > blkiowait? So, should other subsystems use it? >=20 > I don't think so. The traditional Unix use of I/O wait is block I/O wait, > in order to account for paging/swapping in "uptime". I see. > The other problem is that if you change the way it behaves you'll get > lots of hate mail from people running server farms as all their load > balancing and cluster management changes behaviour, plus baffled users > wondering why their system is now busy and it wasn't in the last release. I was fearing something like that. On the other hand, it might have been more correct. That's why I asked. > The other question you have to solve is that people are adding i2c and > SPI slave support both in Android space and now perhaps upstream. How do > you I/O account those transactions ? I implemented I2C slave support for upstream [1] and I don't think it needs to be acocunted. While a master transaction gets kicked off and then waits for success using a completion, slave support is more like serving an interrupt and then getting or putting a byte immediately. Thanks for your answers, I'll simply keep I2C away from iowait. Wolfram [1] http://thread.gmane.org/gmane.linux.kernel/1783295 --hQiwHBbRI9kgIhsi Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUV9tCAAoJEBQN5MwUoCm2r0MP/RpOv/f1fId2+ZltT4H7ws2f e2y/DMaK/Fp3/11p18lPd/l4VlYOFcCMsT8qTuRYyodDn9NZU3lUE2QWZAD+NXNy TJMqhT9D2lWn9gTQ4wzgxSdQ6XduEyhpDEVxZqK9PMjU36gXwfc2fE4JBz9oZ6vs tAXHnZQMBqIJKrH+puoPrdk3q1CPpy2PaQKrJ/OzqlLWJ0bAYx4gm73S2Ia02GRN eCz2oLYpQ32B/g3uIhsw9/GS7DFw5poLoG97s3a9TL5yisJJAMHz+IrZoz+dpiXj mQwFBZnC2GLrX6eXsG/WgDPtKhgXOQHLNQWbMSuVNTiojifnTge0Vu+JXC6Alc8t lKcboppvH+4JjV3fWwVrx6lo6xKWix5/KPEva95DxRWXXCdBJTtCx/xIBw2sKC4X BJY1CMkCnnoTjbpPy60PkEGKLeE49hM7oMsbDiDrCrrv2IA8qJ1qaGHZM6yIeMgk zM3w2ZPyAeBfKGp47B3wijmpLJl5mpYNxE28L1iaxlmPSwqaJpexVCcEvZseLLnF ykGFhajbQIb15YReUoS4wbn0eUwpK/iejDHaTQ7F001ZC6Uz1mTEkAvYYGyhAOiv FAh46TIHS6kHVWpKXaCu9CRaufjQPdyzgGLp21ejqHCYZdphhVIRw9ofPoUy6OdP SEc3NU53/PZYog7Ai2qv =tx1S -----END PGP SIGNATURE----- --hQiwHBbRI9kgIhsi-- -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html