netdev - Re: [PATCH] net: make CONFIG_BQL actually end user configurable

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Date:	Mon, 5 Mar 2012 21:57:40 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	Dave Taht <dave.taht@...il.com>, davem@...emloft.net,
	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: make CONFIG_BQL actually end user configurable

>> 1) There is no way to tell if a driver has it actually enabled or not
>> at run time.
>
> In a similar vein, I was interested in a (quick) way to tell if a
> driver has it actually enabled *correctly*.  I'd coded up the basic
> changes for a common PPC NIC, but I was then left wondering what I
> could use as a quick high-water-mark to see if I'd really managed
> to implement it correctly via some level of real run-time testing.
>
The sysfs variables should be good to view the operation and effects
of BQL.  To disable BQL (at least limit checking) "echo max >
limit_min" should be sufficient.

It is true there is no way to determine that BQL is implement for a
device, the sysfs variables are always created.  If it is
unimplemented then inflight and limit variables are always zero.

> If we want to get driver authors involved in adding support to their
> favourite hardware, some description of a basic sanity test would
> probably be a worthwhile description to have.

That would be good.  The best window into BQL is the sysfs variables
(inflight and limit).  Setting zero or max to limit_min should impact
the number of queued bytes being reported.  ("watch cat *" in tx-0I'm
still intending to get the document on BQL out, the sanity check would
be good to describe there I think.

Thanks,
Tom
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