netdev - Re: [PATCH v3 net-next] liquidio: improve UDP TX performance

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Date:   Thu, 09 Mar 2017 13:08:35 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     felix.manlunas@...ium.com
Cc:     netdev@...r.kernel.org, raghu.vatsavayi@...ium.com,
        derek.chickles@...ium.com, satananda.burla@...ium.com,
        veerasenareddy.burru@...ium.com
Subject: Re: [PATCH v3 net-next] liquidio: improve UDP TX performance

From: Felix Manlunas <felix.manlunas@...ium.com>
Date: Mon, 6 Mar 2017 18:45:59 -0800

> Improve UDP TX performance by:
> * reducing the ring size from 2K to 512
> * replacing the numerous streaming DMA allocations for info buffers and
>   gather lists with one large consistent DMA allocation per ring

I applied this, because one should always use consistent mappings for
descriptor arrays and things like this, however I am confused about
this:

> Also, finding an empty entry (in rbtree of device domain's iova mapping in
> kernel) during Tx path becomes a bottleneck every so often; the loop to
> find the empty entry goes through over 40K iterations;

A properly balanced tree should not require 40K iterations for a search.