linux-kernel - Re: stmmac: turn coalescing / NAPI off in stmmac

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Date:   Fri, 2 Dec 2016 16:31:25 +0100
From:   Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:     Pavel Machek <pavel@....cz>
CC:     David Miller <davem@...emloft.net>, <alexandre.torgue@...com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: stmmac: turn coalescing / NAPI off in stmmac

Hi Pavel

On 12/2/2016 11:42 AM, Pavel Machek wrote:
> Hi!
>
>>> Anyway... since you asked. I belive I have way to disable NAPI / tx
>>> coalescing in the driver. Unfortunately, locking is missing on the rx
>>> path, and needs to be extended to _irqsave variant on tx path.
>>
>> I have just replied to a previous thread about that...
>
> Yeah, please reply to David's mail where he describes why it can't
> work.

let me to re-check the mails :-) I can try to provide you
more details about what I experimented

>
>>> So patch currently looks like this (hand edited, can't be
>>> applied, got it working few hours ago). Does it look acceptable?
>>>
>>> I'd prefer this to go after the patch that pulls common code to single
>>> place, so that single place needs to be patched. Plus I guess I should
>>> add ifdefs, so that more advanced NAPI / tx coalescing code can be
>>> reactivated when it is fixed. Trivial fixes can go on top. Does that
>>> sound like a plan?
>>
>> Hmm, what I find strange is that, just this code is running since a
>> long time on several platforms and Chip versions. No raise condition
>> have been found or lock protection problems (also proving look
>> mechanisms).
>
> Well, it works better for me when I disable CONFIG_SMP. It is normal
> that locking problems are hard to reproduce :-(.

can you share me the test, maybe I can try to reproduce on ARM box.
Are you using 3.x or 4.x GMAC?

>> Pavel, I ask you sorry if I missed some problems so, if you can
>> (as D. Miller asked) to send us a cover letter + all patches
>> I will try to reply soon. I can do also some tests if you ask
>> me that! I could run on 3.x and 4.x but I cannot promise you
>> benchmarks.
>
> Actually... I have questions here. David normally pulls from you (can
> I have a address of your git tree?).

No I send the patches to the mailing list.

>
> Could you apply these to your git?
>
> [PATCH] stmmac ethernet: unify locking
> [PATCH] stmmac: simplify flag assignment
> [PATCH] stmmac: cleanup documenation, make it match reality
>
> They are rather trivial and independend, I'm not sure what cover
> letter would say, besides "simple fixes".
>
> Then I can re-do the reset on top of that...
>
>>> Which tree do you want patches against?
>>>
>>> https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/ ?
>>
>> I think that bug fixing should be on top of net.git but I let Miller
>> to decide.
>
> Hmm. It is "only" a performance problem (40msec delays).. I guess
> -next is better target.

ok, maybe if you resend these with a cover-letter I can try to
contribute on reviewing (in case of I have missed some detail).

Best Regards
Peppe

>
> Best regards,
> 								Pavel
>