netdev - Re: Strange latency spikes/TX network stalls on Sun Fire X4150(x86) and e1000e

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Message-ID: <CA+mtBx8fpS_w7X2iq+tOEFuFhhgJ-4V_1ubBsd8-MvvmCef45w@mail.gmail.com>
Date:	Fri, 25 May 2012 09:59:37 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Denys Fedoryshchenko <denys@...p.net.lb>, netdev@...r.kernel.org
Subject: Re: Strange latency spikes/TX network stalls on Sun Fire X4150(x86)
 and e1000e

> TX completion has no budget, I am not sure what you mean.
>
Right, it's the budget on RX that can be a factor.  TX completion is
done from the NAPI poll routine, so if RX does not complete the NAPI
is rescheduled and TX completion is done again for the same HW
interrupt.

We need to remove the constraint that netdev_completed can only be
called once per interrupt...

Tom

> e1000e driver indeed has a limit : It cannot clean more than
> tx_ring->count frames per e1000_clean_tx_irq() invocation.
>
> But with BQL, this should not happen ?
>
> # ethtool -g eth0
> Ring parameters for eth0:
> Pre-set maximums:
> RX:             4096
> RX Mini:        0
> RX Jumbo:       0
> TX:             4096
> Current hardware settings:
> RX:             256
> RX Mini:        0
> RX Jumbo:       0
> TX:             256
>
>
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