Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422814AbaKNW1d (ORCPT ); Fri, 14 Nov 2014 17:27:33 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:60846 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1161920AbaKNW1b (ORCPT ); Fri, 14 Nov 2014 17:27:31 -0500 From: "Rafael J. Wysocki" To: paulmck@linux.vnet.ibm.com Cc: Konstantin Khlebnikov , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, Len Brown , Tom Boshoven , x86@kernel.org, Josh Triplett , Alexander Monakov Subject: Re: [PATCH v2] ACPI/osl: speedup grace period in acpi_os_map_cleanup Date: Fri, 14 Nov 2014 23:48:30 +0100 Message-ID: <18413590.CmnVIhvXn9@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20141109220038.GH4901@linux.vnet.ibm.com> References: <20141108094717.9388.34638.stgit@zurg> <20141109105337.4952.36899.stgit@zurg> <20141109220038.GH4901@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sunday, November 09, 2014 02:00:38 PM Paul E. McKenney wrote: > On Sun, Nov 09, 2014 at 01:53:37PM +0400, Konstantin Khlebnikov wrote: > > ACPI maintains cache of ioremap regions to speed up operations and > > access to them from irq context where ioremap() calls aren't allowed. > > This code abuses synchronize_rcu() on unmap path for synchronization > > with fast-path in acpi_os_read/write_memory which uses this cache. > > > > Since v3.10 CPUs are allowed to enter idle state even if they have RCU > > callbacks queued, see commit c0f4dfd4f90f1667d234d21f15153ea09a2eaa66 > > ("rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks"). > > That change caused problems with nvidia proprietary driver which calls > > acpi_os_map/unmap_generic_address several times during initialization. > > Each unmap calls synchronize_rcu and adds significant delay. Totally > > initialization is slowed for a couple of seconds and that is enough to > > trigger timeout in hardware, gpu decides to "fell off the bus". Widely > > spread workaround is reducing "rcu_idle_gp_delay" from 4 to 1 jiffy. > > > > This patch replaces synchronize_rcu() with synchronize_rcu_expedited() > > which is much faster. > > > > Signed-off-by: Konstantin Khlebnikov > > Reported-and-tested-by: Alexander Monakov > > Cc: Tom Boshoven > > Link: https://devtalk.nvidia.com/default/topic/567297/linux/linux-3-10-driver-crash/ > > Reviewed-by: Paul E. McKenney Patch queued up for 3.19, thanks! > > > --- > > drivers/acpi/osl.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c > > index 9964f70..217713c 100644 > > --- a/drivers/acpi/osl.c > > +++ b/drivers/acpi/osl.c > > @@ -436,7 +436,7 @@ static void acpi_os_drop_map_ref(struct acpi_ioremap *map) > > static void acpi_os_map_cleanup(struct acpi_ioremap *map) > > { > > if (!map->refcount) { > > - synchronize_rcu(); > > + synchronize_rcu_expedited(); > > acpi_unmap(map->phys, map->virt); > > kfree(map); > > } > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/