netdev - Re: [PATCH net-next] pktgen: Fill the payload optionally with a pattern

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Date:	Fri, 27 Jun 2014 10:01:23 +0100
From:	Zoltan Kiss <zoltan.kiss@...aman.hu>
To:	David Miller <davem@...emloft.net>
CC:	steffen.klassert@...unet.com, minipli@...glemail.com,
	dborkman@...hat.com, tgraf@...g.ch, joe@...ches.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH net-next] pktgen: Fill the payload optionally with a pattern

On 26/06/14 01:54, David Miller wrote:
> From: Zoltan Kiss <zoltan.kiss@...rix.com>
> Date: Tue, 24 Jun 2014 21:40:15 +0100
>
>> Introduces a new flag called PATTERN, which puts a non-periodic, predicatble
>> pattern into the payload. This was useful to reproduce an otherwise intermittent
>> bug in xen-netback [1], where checksum checking doesn't help.
>> The pattern is a repetition of " %lu", a series of increasing numbers divided by
>> space. The value of the number is the size of the preceding payload area. E.g.
>> " 1 3 5"..." 1000 1005 1010"
>> If the pattern is used, every frag will have its own page, unlike before, so it
>> needs more memory.
>>
>> [1] 5837574: xen-netback: Fix grant ref resolution in RX path
>>
>> Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>
> You are changing the page allocation strategy regardless of the pattern
> setting, this is undesirable.
>
> It may be significantly faster to use the same page for all the frags,
> and this is absolutely critical for pktgen usage where every nanosecond
> of performance counts.
If the PATTERN flag is not used, it always using the pages[0] page, so 
it falls back to the original way.

Zoli
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