From mboxrd@z Thu Jan 1 00:00:00 1970 From: Giuseppe CAVALLARO Subject: Re: [net-next.git 3/8 (V2)] stmmac: add the initial tx coalesce schema Date: Fri, 14 Sep 2012 09:36:30 +0200 Message-ID: <5052DE7E.8070704@st.com> References: <1347346514-23411-1-git-send-email-peppe.cavallaro@st.com> <1347346514-23411-4-git-send-email-peppe.cavallaro@st.com> <20120913.162333.1518469374321928795.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, bhutchings@solarflare.com To: David Miller Return-path: Received: from eu1sys200aog118.obsmtp.com ([207.126.144.145]:57525 "EHLO eu1sys200aog118.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756578Ab2INHgu (ORCPT ); Fri, 14 Sep 2012 03:36:50 -0400 In-Reply-To: <20120913.162333.1518469374321928795.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On 9/13/2012 10:23 PM, David Miller wrote: > From: Giuseppe CAVALLARO > Date: Tue, 11 Sep 2012 08:55:09 +0200 > >> + unsigned long flags; >> + >> + spin_lock_irqsave(&priv->tx_lock, flags); >> >> - spin_lock(&priv->tx_lock); >> + priv->xstats.tx_clean++; > > You are changing the locking here for the sake of the new timer. > > But timers run in software interrupt context, so this change is > completely unnecessary since NAPI runs in software interrupt context > as well, and neither timers nor NAPI run in hardware interrupts > context. Indeed It can be called by the ISR too in this new implementation. I have added the spin_lock_irqsave/restore otherwise, testing with CONFIG_PROVE_LOOKING, I get the following warning on ARM SMP. [ 8.030000] [ 8.030000] ================================= [ 8.030000] [ INFO: inconsistent lock state ] [ 8.030000] 3.4.7_stm24_0302-b2000+ #103 Not tainted [ 8.030000] --------------------------------- [ 8.030000] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. [ 8.030000] swapper/0/1 [HC1[1]:SC0[0]:HE0:SE1] takes: [ 8.030000] (&(&priv->tx_lock)->rlock){?.-...}, at: [<802651d8>] stmmac_tx+0x1c/0x388 [ 8.030000] {HARDIRQ-ON-W} state was registered at: [ 8.030000] [<800562b4>] __lock_acquire+0x638/0x179c [ 8.030000] [<80057884>] lock_acquire+0x60/0x74 [ 8.030000] [<80428a08>] _raw_spin_lock+0x40/0x50 [ 8.030000] [<802651d8>] stmmac_tx+0x1c/0x388 [ 8.030000] [<80026be0>] run_timer_softirq+0x180/0x23c [ 8.030000] [<80020ccc>] __do_softirq+0xa0/0x114 [ 8.030000] [<80021204>] irq_exit+0x58/0x7c [ 8.030000] [<8000dc80>] handle_IRQ+0x7c/0xb8 [ 8.030000] [<80008464>] gic_handle_irq+0x34/0x58 [ 8.030000] [<80429684>] __irq_svc+0x44/0x78 [ 8.030000] [<8001c3f4>] vprintk+0x41c/0x480 [ 8.030000] [<8042097c>] printk+0x18/0x24 [ 8.030000] [<805aef6c>] prepare_namespace+0x1c/0x1a4 [ 8.030000] [<805ae980>] kernel_init+0x1c8/0x20c [ 8.030000] [<8000deb8>] kernel_thread_exit+0x0/0x8 [ 8.030000] irq event stamp: 254745 [ 8.030000] hardirqs last enabled at (254744): [<80429240>] _raw_spin_unlock_irqrestore+0x3c/0x6c [ 8.030000] hardirqs last disabled at (254745): [<80429674>] __irq_svc+0x34/0x78 [ 8.030000] softirqs last enabled at (254741): [<8035d964>] dev_queue_xmit+0x6a4/0x724 [ 8.030000] softirqs last disabled at (254737): [<8035d2d4>] dev_queue_xmit+0x14/0x724 [ 8.030000] [ 8.030000] other info that might help us debug this: [ 8.030000] Possible unsafe locking scenario: [ 8.030000] [ 8.030000] CPU0 [ 8.030000] ---- [ 8.030000] lock(&(&priv->tx_lock)->rlock); [ 8.030000] [ 8.030000] lock(&(&priv->tx_lock)->rlock); [ 8.030000] [ 8.030000] *** DEADLOCK *** > Therefore, disabling hardware interrupts for this lock is unnecessary > and will decrease performance. > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >