netdev - Re: irq disable in __netdev_alloc

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Message-ID: <CAMEtUuytvhHJEGCmwkgH9EesCJdDhOn=5AujFymWPxg7g+E3og@mail.gmail.com>
Date:	Wed, 22 Oct 2014 21:29:22 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: irq disable in __netdev_alloc_frag() ?

On Wed, Oct 22, 2014 at 8:56 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2014-10-22 at 20:51 -0700, Eric Dumazet wrote:
>> On Wed, 2014-10-22 at 20:19 -0700, Alexander Duyck wrote:
>>
>> > Couldn't __netdev_alloc_frag() be forked into two functions, one that is
>> > only called from inside the NAPI context and one that is called for all
>> > other contexts?  It would mean having to double the number of pages
>> > being held per CPU, but I would think something like that would be doable.
>>
>> Possibly, but this looks like code bloat for me.
>>
>> On my hosts, this hard irq masking is pure noise.
>>
>> What CPU are you using Alexander ?
>
> Sorry, the question was for Alexei ;)

my numbers were from just released Xeon E5-1630 v3
which is haswell-ep
I think Alexander's idea is worth pursuing.
Code-wise the bloat is minimal: one extra netdev_alloc_cache
and few 'if' which one to choose.
Most of the time only one of them is used, since
systems with napi and not-napi nics are very rare.
I think it should help virtualization case as well,
since virtio_net is napi already.
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