netdev - Re: [PATCH net-next] net: introduce napi_schedule

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Message-ID: <CAADnVQLFZopMmFFpu3B-wBT=8vOWG=Oy3PO+pGcykZsfKd3sBg@mail.gmail.com>
Date:	Wed, 29 Oct 2014 08:26:16 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: introduce napi_schedule_irqoff()

On Tue, Oct 28, 2014 at 11:20 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2014-10-28 at 22:13 -0700, Alexei Starovoitov wrote:
>
>> tried 50 parallel netperf -t TCP_RR over ixgbe
>> and perf top were tcp stack bits, qdisc locks and netperf itself.
>> What do you see?
>
> You are kidding right ?
>
> If you save 30 nsec ( 2 * 15 nsec) per transaction, and rtt is about 20
> usec, its a 0.15 % gain. Not bad for a trivial patch.

agreed.
I wasn't arguing against the patch at all. Was just curious
what performance gain we'll see. 0.15% is tiny and some might
say the code bloat is not worth it, but imo it's a good one. ack.

> Every atomic op we remove/avoid, every irq masking unmasking we remove,
> every cache line miss or extra bus transaction we remove, TLB miss, is
> the path for better latency.

yes. We're saying the same thing.
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