netdev - Re: [PATCH RFC 01/11] net/mlx5e: Single flow order-0 pages for Striding RQ

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Message-ID: <20160907173131.GA64688@ast-mbp.thefacebook.com>
Date:   Wed, 7 Sep 2016 10:31:33 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        netdev@...r.kernel.org, Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Tom Herbert <tom@...bertland.com>,
        Martin KaFai Lau <kafai@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH RFC 01/11] net/mlx5e: Single flow order-0 pages for
 Striding RQ

On Wed, Sep 07, 2016 at 03:42:22PM +0300, Saeed Mahameed wrote:
> From: Tariq Toukan <tariqt@...lanox.com>
> 
> To improve the memory consumption scheme, we omit the flow that
> demands and splits high-order pages in Striding RQ, and stay
> with a single Striding RQ flow that uses order-0 pages.
> 
> Moving to fragmented memory allows the use of larger MPWQEs,
> which reduces the number of UMR posts and filler CQEs.
> 
> Moving to a single flow allows several optimizations that improve
> performance, especially in production servers where we would
> anyway fallback to order-0 allocations:
> - inline functions that were called via function pointers.
> - improve the UMR post process.
> 
> This patch alone is expected to give a slight performance reduction.
> However, the new memory scheme gives the possibility to use a page-cache
> of a fair size, that doesn't inflate the memory footprint, which will
> dramatically fix the reduction and even give a huge gain.
> 
> We ran pktgen single-stream benchmarks, with iptables-raw-drop:
> 
> Single stride, 64 bytes:
> * 4,739,057 - baseline
> * 4,749,550 - this patch
> no reduction
> 
> Larger packets, no page cross, 1024 bytes:
> * 3,982,361 - baseline
> * 3,845,682 - this patch
> 3.5% reduction
> 
> Larger packets, every 3rd packet crosses a page, 1500 bytes:
> * 3,731,189 - baseline
> * 3,579,414 - this patch
> 4% reduction

imo it's not a realistic use case, but would be good to mention that
patch 3 brings performance back for this use case anyway.