netdev - Re: [PATCH] crypto: talitos: Avoid excessive loops in softirq context

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Message-ID: <CAGXE3d9WEyyMSCjj-8bC59x4CxXjaR4Tdfaa+Kauynbz0o7CEw@mail.gmail.com>
Date:	Mon, 15 Sep 2014 10:40:38 +0200
From:	Helmut Schaa <helmut.schaa@...glemail.com>
To:	Kim Phillips <kim.phillips@...escale.com>
Cc:	linux-crypto@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	Sandeep Malik <Sandeep.Malik@...escale.com>,
	Horia Geanta <horia.geanta@...escale.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] crypto: talitos: Avoid excessive loops in softirq context

On Sat, Sep 13, 2014 at 1:21 AM, Kim Phillips
<kim.phillips@...escale.com> wrote:
> [adding Sandeep, Horia and netdev]
>
> On Fri, 12 Sep 2014 09:39:12 +0200
> Helmut Schaa <helmut.schaa@...glemail.com> wrote:
>
>> On Fri, Sep 12, 2014 at 2:49 AM, Kim Phillips
>> <kim.phillips@...escale.com> wrote:
>> > On Wed, 10 Sep 2014 10:34:47 +0200
>> > Helmut Schaa <helmut.schaa@...glemail.com> wrote:
>> >
>> >> The talitos driver can cause starvation of other softirqs and as such
>> >> it can also cause rcu stalls like:
>> > ...
>> >> Work around this by processing a maximum amount of 16 finished requests
>> >> and rescheduling the done-tasklet if any work is left.
>> >> This allows other softirqs to run.
>> >
>> > 16 sounds rather arbitrary, and application-dependent - talitos'
>> > FIFO size is 24.
>>
>> Yep, 16 is arbitrary, I can also do "fifo_len" if you prefer?
>>
>> > IIRC, netdev's NAPI can be refactored out of just being able to work
>> > on network devices, and be made to apply to crypto devices, too.  In
>> > fact, some old Freescale hacks of this nature have improved
>> > performance.  Can we do something like refactor NAPI instead?
>>
>> That would indeed be nice but sounds like quite some more work and
>> I won't have time to do so. Especially since my system was taken down
>> completely by the talitos tasklet under some circumstances. If there is
>> any work going on in that regard I'd be fine with just dropping that patch
>> (and carrying it myself until the refactoring is done).
>
> I'm not aware of any, but to prove whether NAPI actually fixes the
> issue, can you try applying this patch:
> http://patchwork.ozlabs.org/patch/146094/

I guess this would fix it too. Will run some tests soon.
Helmut
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