netdev - Re: Performance regression on kernels 3.10 and newer

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Date:	Fri, 15 Aug 2014 15:16:50 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: Performance regression on kernels 3.10 and newer

On Fri, Aug 15, 2014 at 12:10 PM, Alexander Duyck
<alexander.h.duyck@...el.com> wrote:
> On 08/15/2014 11:49 AM, Tom Herbert wrote:
>> Alex, I tried to repro your problem running your script (on bnx2x).
>> Didn't see see the issue and in fact ip_dest_check did not appear in
>> top perf functions on perf. I assume this is more related to the
>> steering configuration rather than the device (although flow director
>> might be a fundamental difference).
>>
>
> So the original script I put out had a typo.  It was supposed to run all
> 60 at the same time, not one at a time.  So make sure you add an
> ampersand to the end of the netperf command line if you run the test so
> that it is 60 at once, not 60 in series.
>
> Also one other thing I had to do was disable tcp_autocork.  Without that
> the test is a large packets test instead of a small packet test.
>
Okay, by running netperf in background, disabling autoconf, and
turning off RPS/RFS I'm able to get ipv4_dst_check to come up in perf;
but t's not nearly as bad as what you've reported though, only about
1.5%. When I applied path to move rt_genid to different cacheline
ipv4_dst_check goes away (ipv4: move rt_genid to different cache
line). Can you try this patch in your setup?

Thanks,
Tom

> Thanks,
>
> Alex
>
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