Issue found in Armada 370: "No buffer space available" error during continuous ping

[Maggie Mae Roxas]

Hi Thomas, Willy.
Good day.

Thank you for your assistance as always.

We are currently testing the attached patch + 3.13.9.
We'll let you know the results as soon as we've conducted enough tests
- latest tomorrow.

Will keep you posted.

Regards,
Maggie Roxas


On Mon, Dec 1, 2014 at 5:58 PM, Willy Tarreau <w at 1wt.eu> wrote:
> Hi Thomas,
>
> On Mon, Dec 01, 2014 at 10:32:21AM +0100, Thomas Petazzoni wrote:
>> If I understood correctly, on RX the interrupt coalescing can be done
>> every X packets, or after N milliseconds. However, on TX, it's only
>> after Y packets, there is no way to configure a delay.
>
> That was my understanding of the datasheet as well.
>
>> But in any case, with NAPI implemented in software, are these hardware
>> interrupt coalescing features very important? As soon as the number of
>> interrupts becomes high, the kernel will disable the interrupt and
>> switch to polling, no?
>
> Absolutely, but despite this, the interrupts still impact the system's
> performance, because instead of waking up the driver once the Tx queue
> is about to be empty (let's say twice per Tx queue), we wake up as often
> as the system supports it. The net effect is a performance loss of about
> 5% on small packets, which is not huge of course, but would rather be
> spent doing some more useful stuff.
>
> Uri gave me a contact at Marvell who knows this device well, I'll ask
> him if there's no other way to work with this chip. Sending an interrupt
> at least when the Tx queue is empty would be nice :-/
>
> Best regards,
> Willy
>