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Subject: Re: svn commit: r294327 - in head/sys: dev/cxgb dev/cxgbe dev/e1000
 dev/hyperv/netvsc dev/ixgbe dev/mxge netinet sys
To: Ryan Stone <rysto32@gmail.com>
References: <201601191533.u0JFXSxf037804@repo.freebsd.org>
 <CAFMmRNz3uXim3H3-sGuBUBs45Jy8p260ywothgp4iFkUcnvnEw@mail.gmail.com>
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From: Hans Petter Selasky <hps@selasky.org>
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Date: Tue, 19 Jan 2016 17:54:16 +0100
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On 01/19/16 17:09, Ryan Stone wrote:
> On Tue, Jan 19, 2016 at 10:33 AM, Hans Petter Selasky <hselasky@freebsd.org>
> wrote:
>
>>
>> +       qsort(lc->lro_mbuf_data, lc->lro_mbuf_count, sizeof(struct mbuf *),
>> +           &tcp_lro_mbuf_compare_header);
>>
>
> In the worst case, qsort() can take O(n**2) time and consume O(n) stack
> space.  Is there a DOS concern here?
>

Hi Ryan,

Is this the case for the qsort() we have in the FreeBSD kernel?

There are other sorting algorithms which can be used instead of qsort() 
which consume O(n * log(n)) time and O(1) stack, but requires a power of 
two set of elements to sort.

--HPS