From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp06.au.ibm.com (e23smtp06.au.ibm.com [202.81.31.148]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 869051A0BF2 for ; Wed, 21 Jan 2015 10:53:43 +1100 (AEDT) Received: from /spool/local by e23smtp06.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Jan 2015 09:53:42 +1000 Received: from d23relay06.au.ibm.com (d23relay06.au.ibm.com [9.185.63.219]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id E68572BB003F for ; Wed, 21 Jan 2015 10:53:40 +1100 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay06.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t0KNreb638731950 for ; Wed, 21 Jan 2015 10:53:40 +1100 Received: from d23av01.au.ibm.com (localhost [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t0KNre2H030279 for ; Wed, 21 Jan 2015 10:53:40 +1100 Date: Wed, 21 Jan 2015 10:53:38 +1100 From: Gavin Shan To: Gavin Shan Subject: Re: [PATCH] powerpc/pseries: Avoid context switch in EEH reset if required Message-ID: <20150120235338.GA5280@shangw> Reply-To: Gavin Shan References: <1421621243-21265-1-git-send-email-gwshan@linux.vnet.ibm.com> <1421746096.4949.40.camel@kernel.crashing.org> <20150120225607.GA12174@shangw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20150120225607.GA12174@shangw> Cc: wenxiong@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jan 21, 2015 at 09:56:07AM +1100, Gavin Shan wrote: >On Tue, Jan 20, 2015 at 10:28:16AM +0100, Benjamin Herrenschmidt wrote: >>On Mon, 2015-01-19 at 09:47 +1100, Gavin Shan wrote: >>> On pseries platform, the EEH reset backend pseries_eeh_reset() can >>> be called in atomic context as follows. For this case, we should >>> call udelay() instead of msleep() to avoid context switching. >>> >>> drivers/scsi/ipr.c::ipr_reset_slot_reset_done() >>> drivers/pci/pci.c::pci_set_pcie_reset_state() >>> arch/powerpc/kernel/eeh.c::pcibios_set_pcie_reset_state() >>> arch/powerpc/platforms/pseries/eeh_pseries.c::pseries_eeh_reset() >> >>It's not acceptable to introduce multi-millisecond delays at interrupt >>time. In fact, we should generally not use udelay in such context. >> >>I understand that this is an exceptional error handling case but it's >>still not right. >> > >Yes, I agree it's unsafe to udelay for multi-milliseconds as the queued >works in atomic context is expected to be completed as soon as possible. > >>Are there many other users of pci_set_pcie_reset_state() at interrupt >>time ? Can we have a discussion with the PCI folks as to whether that >>should be legal or not ? >> >>I'm tempted to require that it's made illegal. > >Currently, there are 2 drivers calling this function: IPR and misc/genwqe. >Also, VFIO would call this function for IBM and Mellanox adapters in PowerKVM >repository. For now, IPR driver is the only one call this function in atomic >context. > >Sure, I'll send one email to confirm with PCI folks. I guess it's illegal >to call pci_set_pcie_reset_state() in atomic context. If it's the case, >I'm afraid Wendy has to change IPR driver to replace the reset timer with >something else (e.g. workqueue). > Another way is to drop the hold/settle delays for pcibios_set_pcie_reset_state() and IPR relies on the timer interval to cover them. Wendy, could you please let me know if it would work for you or not? Start reset timer; Timer expires, assert the reset. Restart the timer with assert delay; Timer expires, deassert the reset. Restart the timer with settle delay; Timer expires, ready for subsequent works; Thanks, Gavin >> >>Ben. >> >>> Signed-off-by: Gavin Shan >>> Tested-by: Wen Xiong >>> --- >>> arch/powerpc/platforms/pseries/eeh_pseries.c | 12 ++++++++---- >>> 1 file changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/powerpc/platforms/pseries/eeh_pseries.c b/arch/powerpc/platforms/pseries/eeh_pseries.c >>> index a6c7e19..67623a3 100644 >>> --- a/arch/powerpc/platforms/pseries/eeh_pseries.c >>> +++ b/arch/powerpc/platforms/pseries/eeh_pseries.c >>> @@ -503,8 +503,7 @@ static int pseries_eeh_get_state(struct eeh_pe *pe, int *state) >>> */ >>> static int pseries_eeh_reset(struct eeh_pe *pe, int option) >>> { >>> - int config_addr; >>> - int ret; >>> + int config_addr, delay, ret; >>> >>> /* Figure out PE address */ >>> config_addr = pe->config_addr; >>> @@ -528,9 +527,14 @@ static int pseries_eeh_reset(struct eeh_pe *pe, int option) >>> /* We need reset hold or settlement delay */ >>> if (option == EEH_RESET_FUNDAMENTAL || >>> option == EEH_RESET_HOT) >>> - msleep(EEH_PE_RST_HOLD_TIME); >>> + delay = EEH_PE_RST_HOLD_TIME; >>> + else >>> + delay = EEH_PE_RST_SETTLE_TIME; >>> + >>> + if (in_atomic()) >>> + udelay(delay * 1000); >>> else >>> - msleep(EEH_PE_RST_SETTLE_TIME); >>> + msleep(delay); >>> >>> return ret; >>> } >> >>