netdev - Re: [net-next.git 3/8 (V2)] stmmac: add the initial tx coalesce schema

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Date:	Tue, 18 Sep 2012 07:41:41 +0200
From:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:	David Miller <davem@...emloft.net>, bhutchings@...arflare.com
Cc:	netdev@...r.kernel.org
Subject: Re: [net-next.git 3/8 (V2)] stmmac: add the initial tx coalesce schema

Hello David, Ben,

On 9/14/2012 9:36 AM, Giuseppe CAVALLARO wrote:
> On 9/13/2012 10:23 PM, David Miller wrote:
>> From: Giuseppe CAVALLARO <peppe.cavallaro@...com>
>> 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.

sorry if I disturb you again, any news on these patches?
Please, let me know.

Regards
Peppe

>
> [    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]   <Interrupt>
> [    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.
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>

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