Re: [PATCH v4 1/3] can: kvaser_usb: Fix tx queue start/stop race conditions

On 03/14/2015 03:38 PM, Ahmed S. Darwish wrote:

quoted

Applied to can. This will go into David's net tree and finally into
net-next. Then I'll apply patches 2+3. Nag me, if I forget about them ;)

Thanks! :-)

So if I've understood correctly, this patch will go to -rc5 and
the rest will go into net-next?

If so, IMHO patch #2 should also go to -rc5. I know it's usually
frowned up on to add further patches at this late -rc stage, but
here's my logic:

The original driver code just _arbitrarily_ assumed a MAX_TX_URB
value of 16 parallel transmissions. This value was chosen, it seems,
because the driver was heavily based on esd_usb2.c and the esd code
just did so :-(

Meanwhile, in the Kvaser hardware at hand, if I've increased the
driver's max parallel transmissions little above the recommended
limit reported by firmware, the firmware breaks up badly, reports a
massive list of internal errors, and the candump traces becomes
sort of an internal mess hardly related to the actual frames sent
and received.

In this particular hardware, what's the limit as reported by the firmware?

In my case, I was lucky that the brand we own here (*) had a higher
max outstanding transmissions value than 16. But if there is hardware

Okay - higher.

out there with a max oustanding tx support < 16 (#), such hardware
will break badly under a heavy transmission load :-(

I see.

If you add this motivation to the patch description and let the subject
reflect that this is a "fix" or safety measure rather than a possible
performance improvement, no-one will say anything against this patch :D

(*) http://www.kvaser.com/products/kvaser-usb-hs-ii-hsls/

(#) There are a huge list of Kvaser products having the same controller
    but with different performance metrics, so this is quite a
    possiblity.

Marc

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