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

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Date:	Fri, 27 Jun 2014 12:30:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	zoltan.kiss@...aman.hu
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

From: Zoltan Kiss <zoltan.kiss@...aman.hu>
Date: Fri, 27 Jun 2014 10:01:23 +0100

> 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.

That's now what I see.

If the size exceeds a page, the current code will use the same page over
and over again.

Your new code always increments 'i' and allocates a new page, regardless
of whether the PATTERN flag is set.

Or do I misread your changes?
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