From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756764AbaEGPRq (ORCPT ); Wed, 7 May 2014 11:17:46 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:56358 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755660AbaEGPRo (ORCPT ); Wed, 7 May 2014 11:17:44 -0400 Date: Wed, 7 May 2014 17:17:35 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, khilman@linaro.org, tglx@linutronix.de, axboe@fb.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:timers/nohz] nohz: Move full nohz kick to its own IPI Message-ID: <20140507151735.GQ30445@twins.programming.kicks-ass.net> References: <20140505123706.GP17778@laptop.programming.kicks-ass.net> <20140505133113.GD1429@laptop.programming.kicks-ass.net> <20140505150356.GB2099@localhost.localdomain> <20140505151228.GR26782@laptop.programming.kicks-ass.net> <20140505153405.GD2099@localhost.localdomain> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="N8NGGaQn1mzfvaPg" Content-Disposition: inline In-Reply-To: <20140505153405.GD2099@localhost.localdomain> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --N8NGGaQn1mzfvaPg Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 05, 2014 at 05:34:08PM +0200, Frederic Weisbecker wrote: > On Mon, May 05, 2014 at 05:12:28PM +0200, Peter Zijlstra wrote: > > > Note the current ordering: > > >=20 > > > cmpxchg(&qsd->pending, 0, 1) get ipi > > > csd_lock(qsd->csd) xchg(&qsd->pending, 1) > > > send ipi csd_unlock(qsd->csd) > > >=20 > > >=20 > > > So there shouldn't be racing updaters. Also ipi sender shouldn't > > > race with ipi receiver, the update shouldn't always eventually see > > > the unlock happening. > >=20 > > Yeah, I've not spotted how this particular train wreck happens either. > >=20 > > The problem is reproduction, it took me 9 hours to confirm I could > > reproduce the problem on my machine. So how long to I run it with this > > patch reverted to show its gone.. >=20 > Maybe it could be favoured cpu hotplug. Anyway converting to irq_work sho= uld > fix it. Ingo needs a commit msg for the revert of this patch; do you think you have time to look into _why_ this patch is broken and write such a thing? --N8NGGaQn1mzfvaPg Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJTak6PAAoJEHZH4aRLwOS69hUQAKlT4ZTa/JCys+vIQ78970gf ao++5cWVha6laKANYHGtoNyIGL0tpEonqMyTiP2+BvL5fCQt2rYYQ0piDkbIDhQs eI3YiCKz8LM/Oee23U9pMeHEnmNAnhvk7pWrNWjzipKeV9x25PKWOk2QV1hT4bP7 qb1q0+iNB3KNipKRwmUSEkwhD3OhoL/b5ylqxW8xzFCuz/mJ1L4kHCjCTWim28Y8 4QcIrNyhDbPBOO6APbIoJo++NQmjVkXTBI9tqNUEdDxqJyEv560IlkfXlqk0bgcA sqJzQgEmRXFpnUUbtGEB+z0Ela0hPzAzBDXCImsT3eT44+XcDY06dB4sk3SJlkZs ww6A2IB3/BLpFMIQmY7TRU8Nwu/b5pdxTQT5xLs+G/cLhKo1/0RkVvpA7tuPBhh0 ZyQwL5C67XAQQgXxudZHxjiFEc0H/AeWkHajHFEMi9HApgdKe2FBlaVLWJsuKypx Z/GD3rII10AGdSKNwWD+iCNfhJc9Ec4RXXyw76LBjPzOFUA/Q9AgXOYTqWGfIke1 6FiUG2rM0snxvgXuQzcW8WLGeknNd3lkuR/ZQ2ZhqrfFuXWZHnWuHj42S3pbvlRo YX7k+To0MAfCktvdZHcd3taiGJISmZ7AK+ByLRpTtbL4nZTBnNjEh+scyIoq0eOQ mQDgAmL6XpngjNBbssJD =sbDR -----END PGP SIGNATURE----- --N8NGGaQn1mzfvaPg--